Bank PO Interview Questions

Q How are you
Q Hope you didn’t get any problem in reaching the venue
Q Had your Breakfast or not.
Q Tell me something about your self
Q Tell me about your Father
Q Tell me about Your family
Q How can you be useful for us as your qualification
Q Why Banking sector you select
Q Difference between Customer Satisfaction And Customer delight
Q What do you think which one is more valuable
Q What are the different Banking products

Bank PO Important interview Questions and Answers

What is the difference between cheque and Demand Draft?

A cheque is basically issued by an individual but a draft is issued by a bank. In a demand draft you have to pay before issuing while a check is withdrawn from the account.

What is the difference between Private bank Nationalized bank?

Nationalized banks are also known as public sector banks where the government is responsible for the deposition of money in these banks while in a private bank money is deposited by the person who owns the bank.

What is sensex and NIFTY?

Sensex and Nifty both are an “index”. Index is like a indicator which gives us a general idea whether the stocks have gone up or have gone down.

Nifty is an index of NSE (National Stock Exchange) while Sensex is an index of BSE (Bomabay Stock exchange)

What is Repo rate and Reverse Repo Rate?

Repo rate is the rate at which the RBI lends some money to the banks while reverse repo rate is the rate at which the RBI takes money from a commercial bank. Repo rate controls inflation.

What is Fiscal deficit?

Fiscal Deficit is a sitation when the total expenditure of the government exceeds the revenue it generates. It is not similar to debt as debt is a collection of yearly defecits.

What is CRR rate?

CRR or Cash Reverse Ratio is the amount of money that a commercial bank has to keep with the Reserve Bank of India. If the bank increase CRR then the amount with RBI comes down and vice-versa.

What is SLR rate?

SLR Rate is the minimum amount or percentage of the deposits that a bank has to keep with the RBI in the form of money,gold or any other approved security. In simple terms it is the ratio between cash and some approved security.

What is Bank Rate?

Bank Rate is the interest rate at which the RBI allows finance to commercial banks. By Bank Rate, we mean bank can regulate the level of economic activity.

Java Collection - Basic Interview Questions and Answers

·  What are Collection related features in Java 8?

Java 8 has brought major changes in the Collection API. Some of the changes are:

1. Java Stream API for collection classes for supporting sequential as well as parallel processing
2. Iterable interface is extended with forEach() default method that we can use to iterate over a collection. It is very helpful when used with lambda expressions because it’s argument Consumer is a function interface.
3. Miscellaneous Collection API improvements such as forEachRemaining(Consumer action) method in Iterator interface, Map replaceAll(), compute(), merge() methods.

·  What is Java Collections Framework? List out some benefits of Collections framework?

Collections are used in every programming language and initial java release contained few classes for collections: Vector, Stack, Hashtable, Array. But looking at the larger scope and usage, Java 1.2 came up with Collections Framework that group all the collections interfaces, implementations and algorithms.
Java Collections have come through a long way with usage of Generics and Concurrent Collection classes for thread-safe operations. It also includes blocking interfaces and their implementations in java concurrent package.
Some of the benefits of collections framework are;

• Reduced development effort by using core collection classes rather than implementing our own collection classes.
• Code quality is enhanced with the use of well tested collections framework classes.
• Reduced effort for code maintenance by using collection classes shipped with JDK.
• Reusability and Interoperability

·  What is the benefit of Generics in Collections Framework?

Java 1.5 came with Generics and all collection interfaces and implementations use it heavily. Generics allow us to provide the type of Object that a collection can contain, so if you try to add any element of other type it throws compile time error.
This avoids ClassCastException at Runtime because you will get the error at compilation. Also Generics make code clean since we don’t need to use casting and instanceof operator. I would highly recommend to go through Java Generic Tutorial to understand generics in a better way.

·  What are the basic interfaces of Java Collections Framework?

Collection is the root of the collection hierarchy. A collection represents a group of objects known as its elements. The Java platform doesn’t provide any direct implementations of this interface.

Set is a collection that cannot contain duplicate elements. This interface models the mathematical set abstraction and is used to represent sets, such as the deck of cards.

List is an ordered collection and can contain duplicate elements. You can access any element from it’s index. List is more like array with dynamic length.

A Map is an object that maps keys to values. A map cannot contain duplicate keys: Each key can map to at most one value.

·  Why Collection doesn’t extend Cloneable and Serializable interfaces?

Collection interface specifies group of Objects known as elements. How the elements are maintained is left up to the concrete implementations of Collection. For example, some Collection implementations like List allow duplicate elements whereas other implementations like Set don’t.
A lot of the Collection implementations have a public clone method. However, it does’t really make sense to include it in all implementations of Collection. This is because Collection is an abstract representation. What matters is the implementation.
The semantics and the implications of either cloning or serializing come into play when dealing with the actual implementation; so concrete implementation should decide how it should be cloned or serialized, or even if it can be cloned or serialized.
So mandating cloning and serialization in all implementations is actually less flexible and more restrictive. The specific implementation should make the decision as to whether it can be cloned or serialized.

·  Why Map interface doesn’t extend Collection interface?

Although Map interface and it’s implementations are part of Collections Framework, Map are not collections and collections are not Map. Hence it doesn’t make sense for Map to extend Collection or vice versa.
If Map extends Collection interface, then where are the elements? Map contains key-value pairs and it provides methods to retrieve list of Keys or values as Collection but it doesn’t fit into the “group of elements” paradigm.

·  What is an Iterator?

Iterator interface provides methods to iterate over any Collection. We can get iterator instance from a Collection using iterator() method. Iterator takes the place of Enumeration in the Java Collections Framework. Iterators allow the caller to remove elements from the underlying collection during the iteration. Java Collection iterator provides a generic way for traversal through the elements of a collection and implements Iterator Design Pattern.

·  What is difference between Enumeration and Iterator interface?

Enumeration is twice as fast as Iterator and uses very less memory. Enumeration is very basic and fits to basic needs. But Iterator is much safer as compared to Enumeration because it always denies other threads to modify the collection object which is being iterated by it.
Iterator takes the place of Enumeration in the Java Collections Framework. Iterators allow the caller to remove elements from the underlying collection that is not possible with Enumeration. Iterator method names have been improved to make it’s functionality clear.

·  Why there is not method like Iterator.add() to add elements to the collection?

The semantics are unclear, given that the contract for Iterator makes no guarantees about the order of iteration. Note, however, that ListIterator does provide an add operation, as it does guarantee the order of the iteration.

·  Why Iterator don’t have a method to get next element directly without moving the cursor?

It can be implemented on top of current Iterator interface but since it’s use will be rare, it doesn’t make sense to include it in the interface that everyone has to implement.

·  What is different between Iterator and ListIterator?

• We can use Iterator to traverse Set and List collections whereas ListIterator can be used with Lists only.
• Iterator can traverse in forward direction only whereas ListIterator can be used to traverse in both the directions.
• ListIterator inherits from Iterator interface and comes with extra functionalities like adding an element, replacing an element, getting index position for previous and next elements.

·  What are different ways to iterate over a list?

We can iterate over a list in two different ways – using iterator and using for-each loop.

1 2 3 4 5 6 7 8 9 10 11

List<String> strList = new ArrayList<>(); //using for-each loop for(String obj : strList){     System.out.println(obj); } //using iterator Iterator<String> it = strList.iterator(); while(it.hasNext()){     String obj = it.next();     System.out.println(obj); }

Using iterator is more thread-safe because it makes sure that if underlying list elements are modified, it will throw ConcurrentModificationException.

·  What do you understand by iterator fail-fast property?

Iterator fail-fast property checks for any modification in the structure of the underlying collection everytime we try to get the next element. If there are any modifications found, it throws ConcurrentModificationException. All the implementations of Iterator in Collection classes are fail-fast by design except the concurrent collection classes like ConcurrentHashMap and CopyOnWriteArrayList.

·  What is difference between fail-fast and fail-safe?

Iterator fail-safe property work with the clone of underlying collection, hence it’s not affected by any modification in the collection. By design, all the collection classes in java.util package are fail-fast whereas collection classes in java.util.concurrent are fail-safe.
Fail-fast iterators throw ConcurrentModificationException whereas fail-safe iterator never throws ConcurrentModificationException.
Check this post for CopyOnWriteArrayList Example.

·  How to avoid ConcurrentModificationException while iterating a collection?

We can use concurrent collection classes to avoid ConcurrentModificationException while iterating over a collection, for example CopyOnWriteArrayList instead of ArrayList.
Check this post for ConcurrentHashMap Example.

·  Why there are no concrete implementations of Iterator interface?

Iterator interface declare methods for iterating a collection but it’s implementation is responsibility of the Collection implementation classes. Every collection class that returns an iterator for traversing has it’s own Iterator implementation nested class.
This allows collection classes to chose whether iterator is fail-fast or fail-safe. For example ArrayList iterator is fail-fast whereas CopyOnWriteArrayList iterator is fail-safe.

·  What is UnsupportedOperationException?

UnsupportedOperationException is the exception used to indicate that the operation is not supported. It’s used extensively in JDK classes, in collections framework java.util.Collections.UnmodifiableCollection throws this exception for all add and remove operations.

·  How HashMap works in Java?

HashMap stores key-value pair in Map.Entry static nested class implementation. HashMap works on hashing algorithm and uses hashCode() and equals() method in put and get methods.

When we call put method by passing key-value pair, HashMap uses Key hashCode() with hashing to find out the index to store the key-value pair. The Entry is stored in the LinkedList, so if there are already existing entry, it uses equals() method to check if the passed key already exists, if yes it overwrites the value else it creates a new entry and store this key-value Entry.

When we call get method by passing Key, again it uses the hashCode() to find the index in the array and then use equals() method to find the correct Entry and return it’s value. Below image will explain these detail clearly.

The other important things to know about HashMap are capacity, load factor, threshold resizing. HashMap initial default capacity is 32 and load factor is 0.75. Threshold is capacity multiplied by load factor and whenever we try to add an entry, if map size is greater than threshold, HashMap rehashes the contents of map into a new array with a larger capacity. The capacity is always power of 2, so if you know that you need to store a large number of key-value pairs, for example in caching data from database, it’s good idea to initialize the HashMap with correct capacity and load factor.

·  What is the importance of hashCode() and equals() methods?

HashMap uses Key object hashCode() and equals() method to determine the index to put the key-value pair. These methods are also used when we try to get value from HashMap. If these methods are not implemented correctly, two different Key’s might produce same hashCode() and equals() output and in that case rather than storing it at different location, HashMap will consider them same and overwrite them.

Similarly all the collection classes that doesn’t store duplicate data use hashCode() and equals() to find duplicates, so it’s very important to implement them correctly. The implementation of equals() and hashCode() should follow these rules.

• If o1.equals(o2), then o1.hashCode() == o2.hashCode()should always be true.
• If o1.hashCode() == o2.hashCode is true, it doesn’t mean that o1.equals(o2) will be true.

·  Can we use any class as Map key?

We can use any class as Map Key, however following points should be considered before using them.

• If the class overrides equals() method, it should also override hashCode() method.
• The class should follow the rules associated with equals() and hashCode() for all instances. Please refer earlier question for these rules.
• If a class field is not used in equals(), you should not use it in hashCode() method.
• Best practice for user defined key class is to make it immutable, so that hashCode() value can be cached for fast performance. Also immutable classes make sure that hashCode() and equals() will not change in future that will solve any issue with mutability.
  For example, let’s say I have a class MyKey that I am using for HashMap key.

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//MyKey name argument passed is used for equals() and hashCode() MyKey key = new MyKey("Pankaj"); //assume hashCode=1234 myHashMap.put(key, "Value"); // Below code will change the key hashCode() and equals() // but it's location is not changed. key.setName("Amit"); //assume new hashCode=7890 //below will return null, because HashMap will try to look for key //in the same index as it was stored but since key is mutated, //there will be no match and it will return null. myHashMap.get(new MyKey("Pankaj"));

• This is the reason why String and Integer are mostly used as HashMap keys.

·  What are different Collection views provided by Map interface?

Map interface provides three collection views:

1. Set keySet(): Returns a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator’s own remove operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.
2. Collection values(): Returns a Collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. If the map is modified while an iteration over the collection is in progress (except through the iterator’s own remove operation), the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.
3. Set: Returns a Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator’s own remove operation, or through the setValue operation on a map entry returned by the iterator) the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Core Java Basic Interview Questions and Answers

Q. What if the main method is declared as private?

Answer:

The program compiles properly but at runtime it will give “Main method not public.” message.

Q. What is meant by pass by reference and pass by value in Java?

Answer:

Pass by reference means, passing the address itself rather than passing the value. Pass by value means passing a copy of the value.

Q. If you’re overriding the method equals() of an object, which other method you might also consider?

Answer:

hashCode()

Q. What is Byte Code?

Or

Q. What gives java it’s “write once and run anywhere” nature?

Answer:

All Java programs are compiled into class files that contain bytecodes. These byte codes can be run in any platform and hence java is said to be platform independent.

Q. Expain the reason for each keyword of public static void main(String args[])?

Answer:

• public – main(..) is the first method called by java environment when a program is executed so it has to accessible from java environment. Hence the access specifier has to be public.
• static : Java environment should be able to call this method without creating an instance of the class , so this method must be declared as static.
• void : main does not return anything so the return type must be void

The argument String indicates the argument type which is given at the command line and arg is an array for string given during command line.

Q. What are the differences between == and .equals() ?

Or

Q. what is difference between == and equals

Or

Q. Difference between == and equals method

Or

Q. What would you use to compare two String variables – the operator == or the method equals()?

Or

Q. How is it possible for two String objects with identical values not to be equal under the == operator?

Answer:

The == operator compares two objects to determine if they are the same object in memory i.e. present in the same memory location. It is possible for two String objects to have the same value, but located in different areas of memory.

== compares references while .equals compares contents. The method public boolean equals(Object obj) is provided by the Object class and can be overridden. The default implementation returns true only if the object is compared with itself, which is equivalent to the equality operator == being used to compare aliases to the object. String, BitSet, Date, and File override the equals() method. For two String objects, value equality means that they contain the same character sequence. For the Wrapper classes, value equality means that the primitive values are equal.

01	public class EqualsTest {
02

03	public static void main(String[] args) {
04

05	String s1 = “abc”;
06	String s2 = s1;

07	String s5 = “abc”;
08	String s3 = new String(”abc”);

09	String s4 = new String(”abc”);
10	System.out.println(”== comparison : ” + (s1 == s5));

11	System.out.println(”== comparison : ” + (s1 == s2));
12	System.out.println(”Using equals method : ” + s1.equals(s2));

13	System.out.println(”== comparison : ” + s3 == s4);
14	System.out.println(”Using equals method : ” + s3.equals(s4));

15	}
16	}

Output

1	== comparison : true
2	== comparison : true

3	Using equals method : true
4	false

5	Using equals method : true

Q. What if the static modifier is removed from the signature of the main method?

Or

Q. What if I do not provide the String array as the argument to the method?

Answer:

Program compiles. But at runtime throws an error “NoSuchMethodError”.

Q. Why oracle Type 4 driver is named as oracle thin driver?

Answer:

Oracle provides a Type 4 JDBC driver, referred to as the Oracle “thin” driver. This driver includes its own implementation of a TCP/IP version of Oracle’s Net8 written entirely in Java, so it is platform independent, can be downloaded to a browser at runtime, and does not require any Oracle software on the client side. This driver requires a TCP/IP listener on the server side, and the client connection string uses the TCP/IP port address, not the TNSNAMES entry for the database name.

Q. What is the difference between final, finally and finalize? What do you understand by the java final keyword?

Or

Q. What is final, finalize() and finally?

Or

Q. What is finalize() method?

Or

Q. What does it mean that a class or member is final?

Answer:

• final – declare constant
• finally – handles exception
• finalize – helps in garbage collection

Variables defined in an interface are implicitly final. A final class can’t be extended i.e., final class may not be subclassed. This is done for security reasons with basic classes like String and Integer. It also allows the compiler to make some optimizations, and makes thread safety a little easier to achieve. A final method can’t be overridden when its class is inherited. You can’t change value of a final variable (is a constant). finalize() method is used just before an object is destroyed and garbage collected. finally, a key word used in exception handling and will be executed whether or not an exception is thrown. For example, closing of open connections is done in the finally method.

Q. What is the Java API?

Answer:

The Java API is a large collection of ready-made software components that provide many useful capabilities, such as graphical user interface (GUI) widgets.

Q. What is the GregorianCalendar class?

Answer:

The GregorianCalendar provides support for traditional Western calendars.

Q. What is the ResourceBundle class?

Answer:

The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program’s appearance to the particular locale in which it is being run.

Q. Why there are no global variables in Java?

Answer:

Global variables are globally accessible. Java does not support globally accessible variables due to following reasons:

• The global variables breaks the referential transparency
• Global variables create collisions in namespace.

Q. How to convert String to Number in java program?

Answer:

The valueOf() function of Integer class is is used to convert string to Number. Here is the code example:

1	String numString = “1000″;
2	int id=Integer.valueOf(numString).intValue();

Q. What is the SimpleTimeZone class?

Answer:

The SimpleTimeZone class provides support for a Gregorian calendar.

Q. What is the difference between a while statement and a do statement?

Answer:

A while statement (pre test) checks at the beginning of a loop to see whether the next loop iteration should occur. A do while statement (post test) checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the loop body at least once.

Q. What is the Locale class?

Answer:

The Locale class is used to tailor a program output to the conventions of a particular geographic, political, or cultural region.

Q. Describe the principles of OOPS.

Answer:

There are three main principals of oops which are called Polymorphism, Inheritance and Encapsulation.

Q. Explain the Inheritance principle.

Answer:

Inheritance is the process by which one object acquires the properties of another object. Inheritance allows well-tested procedures to be reused and enables changes to make once and have effect in all relevant places

Q. What is implicit casting?

Answer:

Implicit casting is the process of simply assigning one entity to another without any transformation guidance to the compiler. This type of casting is not permitted in all kinds of transformations and may not work for all scenarios.

Example

1	int i = 1000;
2	long j = i; //Implicit casting

Q. Is sizeof a keyword in java?

Answer:

The sizeof is not a keyword.

Q. What is a native method?

Answer:

A native method is a method that is implemented in a language other than Java.

Q. In System.out.println(), what is System, out and println?

Answer:

System is a predefined final class, out is a PrintStream object and println is a built-in overloaded method in the out object.

Q. What are Encapsulation, Inheritance and Polymorphism

Or

Q. Explain the Polymorphism principle. Explain the different forms of  Polymorphism.

Answer:

Polymorphism in simple terms means one name many forms. Polymorphism enables one entity to be used as a general category for different types of actions. The specific action is determined by the exact nature of the situation.

Polymorphism exists in three distinct forms in Java:

• Method overloading
• Method overriding through inheritance
• Method overriding through the Java interface

Q. What is explicit casting?

Answer:

Explicit casting in the process in which the complier are specifically informed to about transforming the object.

Example

1	long i = 700.20;
2	int j = (int) i; //Explicit casting

Q. What is the Java Virtual Machine (JVM)?

Answer:

The Java Virtual Machine is software that can be ported onto various hardware-based platforms

Q. What do you understand by downcasting?

Answer:

The process of Downcasting refers to the casting from a general to a more specific type, i.e. casting down the hierarchy

Q. What are Java Access Specifiers?

Or

Q. What is the difference between public, private, protected and default Access Specifiers?

Or

Q. What are different types of access modifiers?

Answer:

Access specifiers are keywords that determine the type of access to the member of a class. These keywords are for allowing privileges to parts of a program such as functions and variables. These are:

• Public: accessible to all classes
• Protected: accessible to the classes within the same package and any subclasses.
• Private: accessible only to the class to which they belong
• Default: accessible to the class to which they belong and to subclasses within the same package

Q. Which class is the superclass of every class?

Answer:

Object.

Q. Name primitive Java types.

Answer:

The 8 primitive types are byte, char, short, int, long, float, double, and boolean. Additional is String.

Q. What is the difference between static and non-static variables?

Or

Q. What are “class variables”?

Or

Q. What is static in java?

Or

Q. What is a static method?

Answer:

A static variable is associated with the class as a whole rather than with specific instances of a class. Each object will share a common copy of the static variables i.e. there is only one copy per class, no matter how many objects are created from it. Class variables or static variables are declared with the static keyword in a class. These are declared outside a class and stored in static memory. Class variables are mostly used for constants. Static variables are always called by the class name. This variable is created when the program starts and gets destroyed when the programs stops. The scope of the class variable is same an instance variable. Its initial value is same as instance variable and gets a default value when it’s not initialized corresponding to the data type. Similarly, a static method is a method that belongs to the class rather than any object of the class and doesn’t apply to an object or even require that any objects of the class have been instantiated. Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can’t override a static method with a non-static method. In other words, you can’t change a static method into an instance method in a subclass.

Non-static variables take on unique values with each object instance.

Q. What is the difference between the boolean & operator and the && operator?

Answer:

If an expression involving the boolean & operator is evaluated, both operands are evaluated, whereas the && operator is a short cut operator. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. If the first operand evaluates to false, the evaluation of the second operand is skipped.

Q. How does Java handle integer overflows and underflows?

Answer:

It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

Q. What if I write static public void instead of public static void?

Answer:

Program compiles and runs properly.

Q. What is the difference between declaring a variable and defining a variable?

Answer:

In declaration we only mention the type of the variable and its name without initializing it. Defining means declaration + initialization. E.g. String s; is just a declaration while String s = new String (”bob”); Or String s = “bob”; are both definitions.

Q. What type of parameter passing does Java support?

Answer:

In Java the arguments (primitives and objects) are always passed by value. With objects, the object reference itself is passed by value and so both the original reference and parameter copy both refer to the same object.

Q. Explain the Encapsulation principle.

Answer:

Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse. Objects allow procedures to be encapsulated with their data to reduce potential interference. One way to think about encapsulation is as a protective wrapper that prevents code and data from being arbitrarily accessed by other code defined outside the wrapper.

Q. What do you understand by a variable?

Answer:

Variable is a named memory location that can be easily referred in the program. The variable is used to hold the data and it can be changed during the course of the execution of the program.

Q. What do you understand by numeric promotion?

Answer:

The Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integral and floating-point operations may take place. In the numerical promotion process the byte, char, and short values are converted to int values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required.

Q. What do you understand by casting in java language? What are the types of casting?

Answer:

The process of converting one data type to another is called Casting. There are two types of casting in Java; these are implicit casting and explicit casting.

Q. What is the first argument of the String array in main method?

Answer:

The String array is empty. It does not have any element. This is unlike C/C++ where the first element by default is the program name. If we do not provide any arguments on the command line, then the String array of main method will be empty but not null.

Q. How can one prove that the array is not null but empty?

Answer:

Print array.length. It will print 0. That means it is empty. But if it would have been null then it would have thrown a NullPointerException on attempting to print array.length.

Q. Can an application have multiple classes having main method?

Answer:

Yes. While starting the application we mention the class name to be run. The JVM will look for the main method only in the class whose name you have mentioned. Hence there is not conflict amongst the multiple classes having main method.

Q. When is static variable loaded? Is it at compile time or runtime? When exactly a static block is loaded in Java?

Answer:

Static variable are loaded when classloader brings the class to the JVM. It is not necessary that an object has to be created. Static variables will be allocated memory space when they have been loaded. The code in a static block is loaded/executed only once i.e. when the class is first initialized. A class can have any number of static blocks. Static block is not member of a class, they do not have a return statement and they cannot be called directly. Cannot contain this or super. They are primarily used to initialize static fields.

Q. Can I have multiple main methods in the same class?

Answer:

We can have multiple overloaded main methods but there can be only one main method with the following signature :

1	public static void main(String[] args) {}

No the program fails to compile. The compiler says that the main method is already defined in the class.

Q. Explain working of Java Virtual Machine (JVM)?

Answer:

JVM is an abstract computing machine like any other real computing machine which first converts .java file into .class file by using Compiler (.class is nothing but byte code file.) and Interpreter reads byte codes.

Q. How can I swap two variables without using a third variable?

Answer:

Add two variables and assign the value into First variable. Subtract the Second value with the result Value. and assign to Second variable. Subtract the Result of First Variable With Result of Second Variable and Assign to First Variable. Example:

1	int a=5,b=10;a=a+b; b=a-b; a=a-b;

An other approach to the same question

You use an XOR swap. (BEST APPROACH) as in case of using above approach it may goes over/under flow. For example:

1	int a = 5; int b = 10;
2	a = a ^ b;

3	b = a ^ b;
4	a = a ^ b;

Q. What is data encapsulation?

Answer:

Encapsulation may be used by creating ‘get’ and ’set’ methods in a class (JAVABEAN) which are used to access the fields of the object. Typically the fields are made private while the get and set methods are public. Encapsulation can be used to validate the data that is to be stored, to do calculations on data that is stored in a field or fields, or for use in introspection (often the case when using javabeans in Struts, for instance). Wrapping of data and function into a single unit is called as data encapsulation. Encapsulation is nothing but wrapping up the data and associated methods into a single unit in such a way that data can be accessed with the help of associated methods. Encapsulation provides data security. It is nothing but data hiding.

Q. What is reflection API? How are they implemented?

Answer:

Reflection is the process of introspecting the features and state of a class at runtime and dynamically manipulate at run time. This is supported using Reflection API with built-in classes like Class, Method, Fields, Constructors etc. Example: Using Java Reflection API we can get the class name, by using the getName method.

Q. Does JVM maintain a cache by itself? Does the JVM allocate objects in heap? Is this the OS heap or the heap maintained by the JVM? Why

Answer:

Yes, the JVM maintains a cache by itself. It creates the Objects on the HEAP, but references to those objects are on the STACK.

Q. What is phantom memory?

Answer:

Phantom memory is false memory. Memory that does not exist in reality.

Q. Can a method be static and synchronized?

Answer:

A static method can be synchronized. If you do so, the JVM will obtain a lock on the java.lang.

Class instance associated with the object. It is similar to saying:

1	synchronized(XYZ.class) {
2	}

Q. What is difference between String and StringTokenizer?

Answer:

A StringTokenizer is utility class used to break up string.

Example:

1	StringTokenizer st = new StringTokenizer(”Hello World”);
2	while (st.hasMoreTokens()) {

3	System.out.println(st.nextToken());
4	}

Output:

1	Hello
2	World

Question: What is transient variable?

Answer:

Transient variable can’t be serialize. For example if a variable is declared as transient in a Serializable class and the class is written to an ObjectStream, the value of the variable can’t be written to the stream instead when the class is retrieved from the ObjectStream the value of the variable becomes null.

Note

01	transient
02

03	identifies a variable not to be written out when an
04

05	instance is serialized  (It can't be copied to remove
06

07	system)
08

09
10

11	volatile
12

13	indicates that the field is used by synchronized threads
14

15	and that the compiler should not attempt to perform
16

17	optimizations with it.
18

19
20

21	When more than one thread share a (volatile) data it is
22

23	checked every time. Every thread keeps the latest value of volatile variable

Question: Name the containers which uses Border Layout as their default layout?

Answer:

Containers which uses Border Layout as their default are: window, Frame and Dialog classes.

Question: What do you understand by Synchronization?

Answer:

Synchronization is a process of controlling the access of shared resources by the multiple threads in such a manner that only one thread can access one resource at a time. In non synchronized multithreaded application, it is possible for one thread to modify a shared object while another thread is in the process of using or updating the object’s value. Synchronization prevents such type of data corruption.

E.g. Synchronizing a function:

1	public synchronized void Method1 () {
2

3	// Appropriate method-related code.
4

5

}

E.g. Synchronizing a block of code inside a function:

1	public myFunction (){
2	synchronized (this) {

3	// Synchronized code here.
4	}

5

}