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Core Java - Interview Questions and Answers for 'Method' - 116 question(s) found - Order By Newest

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 Q1. How can we run a java program without making any object?Core Java
Anonymous
Ans. By putting code within static method. With Java 6 and earlier versions, even static block can be used.

  Sample Code for static block

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Frequently asked to fresh graduates and less experienced.
 Q2. Why do we write public static void main ? Can we use some other syntax too for main ?Core Java
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Ans.
1. public is the access modifier that makes the method accessible from anywhere, static is the keyword that makes it accessible even without creating any object and using class name only , void means it doesnt return anything , String args[] is the array of argument that this method receives.

2. If I use Main , it will compile correctly as Java will treat it as just another method but it wont be the method "main" which Java looks for when it looks to execute the class and hence will throw

Error: Main method not found in class , please define the main method as:
public static void main(String[] args)

3. Main is not a keyword but a special string that Java looks for while initiating the main thread.

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 Q3. What are the advantages and disadvantages of static variables and static methods ?Core Java
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Ans. Advantages

Can do meta object operations ( like validating something before creating objects , keep count of number of objects )

Can do operations which have nothing to do with objects but still you want them to be tied to Class.

Disadvantages

Commonly used to static variables sometime leads to problems due to access by different objects.

Are not tied to objects so doesn't reflect pure Object Oriented approach.

Needs to be synchronized so as to avoid update conflicts by mutiple objects and threads.

Some limitation in testing as not all frameworks have facility to mock them. Powermock has but Mockito doesnt

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q4. What is a final method ?Core Java
Anonymous
Ans. Its a method which cannot be overridden. Compiler throws an error if we try to override a method which has been declared final in the parent class.

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 Q5. Can we access instance variables within static methods ?Core Java
Anonymous
Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited.

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 Q6. Which of the following is false about main method ?

a. It should be declared public and static
b. it should have only 1 argument of type String array
c. We can override main method
d. We can overload main method
Core Java
Anonymous
Ans. We can override main method

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 Q7. Can we have multiple main methods in a single class ?Core Java2017-01-12 11:00:02

Ans. We can overload the main method by specifying different argument types. For example -

2 main methods with different arguments is perfectly legal

public static void main();
public static void main(String[] args);

The following are not legal as compiler will complain of duplicate methods

public static void main(String[] args);
public static void main(String[] args);

Even The following are not legal as we cannot overload on return types

public static String main(String[] args);
public static void main(String[] args);

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 Q8. Which of the following are valid declarations

1. void method(int... x){};
2. void method(int.. x){};
3. void method(int.. .x){};
4. void method(int ...x){};
5. void method(int... x){};
6. void method(int ... x){};
7. void method(int x, int... y){};
8. void method(int... x, int y){};
9. void method(int... x,int... y){};
Core Java2017-05-22 21:22:57

Ans. 1st is a valid and standard declaration.

2nd results in compilation error as only 2 dots are there.

3rd results in compilation error as three dots are not consecutive and broken.

4 through 6 may not be standard and ideal way of declarations but they are valid and will compile and work fine.

7 is valid declaration.

8 and 9 will result in compilation error as var args can only be provided to last argument.

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 Q9. Why can't we have diamond problem with interfaces ?Core Java2017-07-30 08:15:33

Ans. Interfaces don't have member elements and method definitions that could cause diamond problem. With Java 8, Interfaces have default method definitions. This could have created diamond problem but Java introduced a compile time check for "duplicate default methods" in case same method is derived from multiple interfaces and no definition is overridden by the class.

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 Q10. Similarity and Difference between static block and static method ?Core Java
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Ans. Both belong to the class as a whole and not to the individual objects. Static methods are explicitly called for execution whereas Static block gets executed when the Class gets loaded by the JVM.

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 Q11. Can we override compareTo method for Enumerations ?Core Java
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Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared.

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 Q12. Difference between parameters and arguments ?Core Java
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Ans. Parameters are the variables that the method is expected to receive along with the method call. Arguments are the values which are passed on while calling the methods.

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 Q13. In which cases , moving methods to utility class could be useful ?Core Java

Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases.

Don't belong to one group through is-a relationship ( You can share through parent class method )

Don't implement a specific interface ( java 8 default methods )

Doesn't involve complex computing as you will be loosing the benefit of object state with just static method.

Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism.

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 Q14. What is the difference between these two method declarations ?

private static void method(String[] arg)

and

private static void method(String... arg)
Core Java2017-05-23 08:41:54

Ans. First expects the argument as a string array whereas second expects variable number of string arguments or a string array.

So we can call both by providing string array as an argument but second can be called with 0 to n string arguments which cannot be done for first.

for example - We can call second method with any of following

method();
method("Hello");
method("Hello","World");
method(new String[4]);


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 Q15. What is a Final Method ?Core Java
Anonymous
Ans. A Method that cannot be overriden in the sub class.

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 Q16. Can we override static methods ? Why ?Core Java
Anonymous
Ans. No.

Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable.

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 Q17. How can we create objects if we make the constructor private ?Core Java
Anonymous
Ans. We can do so through a static public member method or static block.

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 Q18. What does String intern() method do?Core Java
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Ans. intern() method keeps the string in an internal cache that is usually not garbage collected.

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 Q19. Will the following program display ""Buggy Bread"" ?

class Test{
   static void display(){
      System.out.println(""Buggy Bread"");
   }
}

class Demo{
   public static void main(String... args){
      Test t = null;
      t.display();
   }
}
Core Java
Admin
info@buggybread.com
Ans.  Yes. static method is not accessed by the instance of class. Either you call it by the class name or the reference.

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  Q20. Can we overload main method in Java ?Core Java
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Ans. Yes, but the overloaded main methods without single String[] argument doesn't get any special status by the JVM. They are just another methods that needs to be called explicitly.

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  Q21. What are Default Methods ?Core Java
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Ans. With Java 8, We can provide method definitions in the Interfaces that gets carried down the classes implementing that interface in case they are not overridden by the Class. Keyword "default" is used to mark the default method.

  Sample Code for interface default

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 Q22. Can we use static method definitions in Interfaces ?Core Java
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Ans. Yes, Effective Java 8.

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 Q23. Why can't we use this in static context ?Core Java
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Ans. Static methods can be called using instance references wherein this would have made sense but static method can also be called using Class name wherein this would mean nothing and hence forbidden.

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 Q24. Can we overload method as following ?

void method(int... x){};
void method(int[] x){};
Core Java2017-05-22 21:27:42

Ans. No. Because java internally treats var args as arrays and hence both method declarations will generate the same byte code and hence would result in ambiguity while determining call binding.

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 Q25. How can we ensure thread safety in static method ?Core Java2017-08-27 07:49:53

Ans. By using synchronized static method or synchronized block

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 Q26. Can static method access instance variables ?Core Java
Anonymous
Ans. Though Static methods cannot access the instance variables directly, They can access them using instance handler.

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 Q27. Does java allow overriding static methods ?Core Java
Anonymous
Ans. No. Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

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 Q28. Explain Method Local Inner Classes ?Core Java
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Ans. You can create a non-static local class inside a body of code. Interfaces cannot have local classes, and you cannot create local interfaces.

Local classes are accessible only from the body of the code in which the class is defined. The local classes are completely inaccessible outside the body of the code in which the class is defined.

You can extend a class or implement interfaces while defining a local class.

A local class can access all the variables available in the body of the code in which it is defined. You can pass only final variables to a local inner class.

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 Q29. What will happen if static modifier is removed from the signature of the main method?
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Ans. Program throws "NoSuchMethodError" error at runtime .

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 Q30. what will be the output of this code ?

public static void main(String[] args){
   StringBuffer s1=new StringBuffer("Buggy");                       
   test(s1);                    
   System.out.println(s1);              
}       

private static void test(StringBuffer s){      
   s.append("Bread");   
}
Core Java
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Ans.  BuggyBread

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 Q31. what will be the output of this code ?

public static void main(String[] args)    {          
   String s1=new String("Buggy");                         
   test(s1);                    
   System.out.println(s1);              
}       

private static void test(StringBuffer s){      
   s.append("Bread");   
}
Core Java
Admin
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Ans.  Buggy

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 Q32. what will be the output of this code ?

public static void main(String[] args)    {          
   StringBuffer s1=new StringBuffer("Buggy");                         
   test(s1);                    
   System.out.println(s1);              
}       

private static void test(StringBuffer s){      
   s=new StringBuffer("Bread");   
}
Core Java
Admin
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Ans.  Buggy

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 Q33. what will be the output ?

class Animal {
public void eat() throws Exception {
}
}

class Dog2 extends Animal {
public void eat(){}
public static void main(){
Animal an = new Dog2();
an.eat();
}
}
Core Java
Admin
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Ans. Compile Time Error: Unhandled exception type Exception

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 Q34. If there is a conflict between Base Class Method definition and Interface Default method definition, Which definition is Picked ?
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Ans. Base Class Definition.

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Rarely asked as default methods have been introduced with Java 8.
 Q35. Can we have a default method without a Body ?Core Java
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Ans. No. Compiler will give error.

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 Q36. Does java allow implementation of multiple interfaces having Default methods with Same name and Signature ?Core Java
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Ans. No. Compilation error.

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Rarely asked as default methods have been introduced with Java 8.
 Q37. Can we have a default method definition in the interface without specifying the keyword "default" ? Core Java
Admin
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Ans. No. Compiler complains that its an abstract method and hence shouldn't have the body.

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 Q38. 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();
}
}
Admin
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Ans. No. Compiler gives error saying "Duplicate Default Methods"

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 Q39. 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();
}
}
Admin
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Ans. Even then the Compiler will give error saying that there is a conflict.

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 Q40. 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");
}
}
Admin
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Ans. There won't be any error and upon execution the overriding class method will be executed.

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