Interview Questions and Answers for 'Java' | Search Interview Question

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Q571. Can we compare Integers by using equals() in Java ?

Core Java

Ans. Yes for the Wrapper class Integer but not for the primitive int.

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Very Frequently asked. Favorite question in walkins and telephonic interviews. Usually among first few questions. Asked in different variants. Must know for intermediate and expert professionals.Among Top 10 frequently asked questions.

Q572. What is rule regarding overriding equals and hashCode method ?

Core Java

Ans. A Class must override the hashCode method if its overriding the equals method.

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Q573. What is the difference between Collection and Collections ?

Core Java

Ans. Collection is an interface whereas Collections is a utility class.

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Q574. Is Java a statically typed or dynamically typed language ?

Ans. Statically typed

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Q575. How can we reverse the order in the TreeMap ?

Ans. Using Collections.reverseOrder()

Map tree = new TreeMap(Collections.reverseOrder());

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Q576. TreeMap orders the elements on which field ?

Ans. Keys

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Q577. How TreeMap orders the elements if the Key is a String ?

Ans. As String implements Comparable, It refers to the String compareTo method to identify the order relationship among those elements.

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Q578. Can we add heterogeneous elements into TreeMap ?

Ans. No, Sorted collections don't allow addition of heterogeneous elements as they are not comparable.

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Q579. Will it create any problem if We add elements with key as user defined object into the TreeMap ?

Ans. It won't create any problem if the objects are comparable i.e we have that class implementing Comparable interface.

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Q580. Can we have null keys in TreeMap ?

Core Java

Ans. No, results in exception.

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Q581. Can value be null in TreeMap ?

Core Java

Ans. Yes.

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Q582. Which interface TreeMap implements ?

Ans. TreeMap implements NavigableMap, SortedMap, Serializable and Clonable.

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Frequently asked in Phone Interviews.

Q583. What are the various Auto Wiring types in Spring ?

Ans. By Name , By Type and Constructor.

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Q584. Is It Good to use Reflection in an application ? Why ?

Core Java

Ans. no, It's like challenging the design of application.

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Q585. Why is Reflection slower ?

Ans. Because it has to inspect the metadata in the bytecode instead of just using precompiled addresses and constants.

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Q586. How many SessionFactory and Session objects are created ?

Java EE

Ans. Single SessionFactory object and multiple session objects for opening different session. Hibernate creates new Session object per thread.

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Q587. What is the difference between int[] x; and int x[]; ?

Core Java

Ans. No Difference. Both are the acceptable ways to declare an array.

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Q588. What are the annotations used in Junit with Junit4 ?

Ans. @Test

The Test annotation indicates that the public void method to which it is attached can be run as a test case.

@Before

The Before annotation indicates that this method must be executed before each test in the class, so as to execute some preconditions necessary for the test.

@BeforeClass

The BeforeClass annotation indicates that the static method to which is attached must be executed once and before all tests in the class.

@After

The After annotation indicates that this method gets executed after execution of each test.

@AfterClass

The AfterClass annotation can be used when a method needs to be executed after executing all the tests in a JUnit Test Case class so as to clean-up the set-up.

@Ignores

The Ignore annotation can be used when you want temporarily disable the execution of a specific test.

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Q589. What is asynchronous I/O ?

Ans. It is a form of Input Output processing that permits other processing to continue before the I/O transmission has finished.

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Q590. If there is a conflict between Base Class Method definition and Interface Default method definition, Which definition is Picked ?

Ans. Base Class Definition.

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Frequently asked these days as there are major changes in Java 8.

Q591. What are new features introduced with Java 8 ?

Core Java

Ans. Lambda Expressions , Interface Default and Static Methods , Method Reference , Parameters Name , Optional , Streams, Concurrency.

Sample Code for Lambda

Sample Code for interface default

Sample Code for Optional

Sample Code for Streams

Sample Code for java.time

Sample Code for Predicate

Sample Code for Consumer

Sample Code for MapMerge

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Rarely asked as default methods have been introduced with Java 8.

Q592. Can we have a default method without a Body ?

Core Java

Ans. No. Compiler will give error.

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Rarely asked as default methods have been introduced with Java 8.

Q593. Can we have a default method definition in the interface without specifying the keyword "default" ?

Core Java

Ans. No. Compiler complains that its an abstract method and hence shouldn't have the body.

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Q594. Can a class implement two Interfaces having default method with same name and signature ?

public interface DefaultMethodInterface {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface");
}
}

public interface DefaultMethodInterface2 {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface2");
}
}

public class HelloJava8 implements DefaultMethodInterface,DefaultMethodInterface2 {
public static void main(String[] args){
DefaultMethodInterface defMethIn = new HelloJava8();
defMethIn.defaultMethod();
}
}

Ans. No. Compiler gives error saying "Duplicate Default Methods"

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Q595. What If we make the method as abstract in another Interface ?

public interface DefaultMethodInterface {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface");
}
}

public interface DefaultMethodInterface2 {
public void defaultMethod(){
System.out.println("DefaultMethodInterface2");
}
}

public class HelloJava8 implements DefaultMethodInterface,DefaultMethodInterface2 {
public static void main(String[] args){
DefaultMethodInterface defMethIn = new HelloJava8();
defMethIn.defaultMethod();
}
}

Ans. Even then the Compiler will give error saying that there is a conflict.

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Q596. What if we override the conflicting method in the Class ?

public interface DefaultMethodInterface {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface");
}
}

public interface DefaultMethodInterface2 {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface2");
}
}

public class HelloJava8 implements DefaultMethodInterface,DefaultMethodInterface2 {
public static void main(String[] args){
DefaultMethodInterface defMethIn = new HelloJava8();
defMethIn.defaultMethod();
}

public void defaultMethod(){
System.out.println("HelloJava8");
}
}

Ans. There won't be any error and upon execution the overriding class method will be executed.

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Q597. What will happen if there is a default method conflict as mentioned above and we have specified the same signature method in the base class instead of overriding in the existing class ?

Ans. There won't be any problem as the Base class method will have precedence over the Interface Default methods.

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Q598. If a method definition has been specified in Class , its Base Class , and the interface which the class is implementing, Which definition will be picked if we try to access it using Interface Reference and Class object ?

Ans. Class method definition is overriding both the definitions and hence will be picked.

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Q599. If a method definition has been specified in the Base Class and the interface which the class is implementing, Which definition will be picked if we try to access it using Interface Reference and Class object ?

Ans. Base Class Definition will have precedence over the Interface Default method definition.

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Q600. Can we access Interface static method using Interface references ?

Ans. No, only using Interface Name.

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