Java Interview Question

Categories: Java 8(JDK1.8)

How many class files are created on compiling the OuterClass in the following program?

public class Person {  

String name, age, address;  

class Employee{  

  float salary=10000;  

}  

class BusinessMen{  

  final String gstin="£4433drt3$";   

}  

public static void main (String args[])  

{  

  Person p = new Person();  

}  

}  


What are anonymous inner classes?

Anonymous inner classes are the classes that are automatically declared and instantiated within an expression. We cannot apply different access modifiers to them. Anonymous class cannot be static, and cannot define any static fields, method, or class. In other words, we can say that it a class without the name and can have only one object that is created by its definition. Consider the following example.


abstract class Person{  

  abstract void eat();  

}  

class TestAnonymousInner{  

 public static void main(String args[]){  

  Person p=new Person(){  

  void eat(){System.out.println("nice fruits");}  

  };  

  p.eat();  

 }  

}  


 What is the nested interface?

An Interface that is declared inside the interface or class is known as the nested interface. It is static by default. The nested interfaces are used to group related interfaces so that they can be easy to maintain. The external interface or class must refer to the nested interface. It can't be accessed directly. The nested interface must be public if it is declared inside the interface but it can have any access modifier if declared within the class. The syntax of the nested interface is given as follows.


interface interface_name{    

 ...    

 interface nested_interface_name{    

  ...    

 }    

}     


Can a class have an interface?

Yes, an interface can be defined within the class. It is called a nested interface.


What is Garbage Collection?

Garbage collection is a process of reclaiming the unused runtime objects. It is performed for memory management. In other words, we can say that It is the process of removing unused objects from the memory to free up space and make this space available for Java Virtual Machine. Due to garbage collection java gives 0 as output to a variable whose value is not set, i.e., the variable has been defined but not initialized. For this purpose, we were using free() function in the C language and delete() in C++. In Java, it is performed automatically. So, java provides better memory management.


What is gc()?

The gc() method is used to invoke the garbage collector for cleanup processing. This method is found in System and Runtime classes. This function explicitly makes the Java Virtual Machine free up the space occupied by the unused objects so that it can be utilized or reused. Consider the following example for the better understanding of how the gc() method invoke the garbage collector.


public class TestGarbage1{  

 public void finalize(){System.out.println("object is garbage collected");}  

 public static void main(String args[]){  

  TestGarbage1 s1=new TestGarbage1();  

  TestGarbage1 s2=new TestGarbage1();  

  s1=null;  

  s2=null;  

  System.gc();  

 }  

}  


How is garbage collection controlled?

Garbage collection is managed by JVM. It is performed when there is not enough space in the memory and memory is running low. We can externally call the System.gc() for the garbage collection. However, it depends upon the JVM whether to perform it or not.


How can an object be unreferenced?

There are many ways:

a) By nulling the reference

b) By assigning a reference to another

c) By anonymous object etc.


What is the purpose of the finalize() method?

The finalize() method is invoked just before the object is garbage collected. It is used to perform cleanup processing. The Garbage collector of JVM collects only those objects that are created by new keyword. So if you have created an object without new, you can use the finalize method to perform cleanup processing (destroying remaining objects). The cleanup processing is the process to free up all the resources, network which was previously used and no longer needed. It is essential to remember that it is not a reserved keyword, finalize method is present in the object class hence it is available in every class as object class is the superclass of every class in java. 


 What is the difference between final, finally and finalize?

No.finalfinallyfinalize

1)Final is used to apply restrictions on class, method, and variable. The final class can't be inherited, final method can't be overridden, and final variable value can't be changed.Finally is used to place important code, it will be executed whether an exception is handled or not.Finalize is used to perform clean up processing just before an object is garbage collected.

2)Final is a keyword.Finally is a block.Finalize is a method.





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