List of Java Keywords with Description

Java Keywords

Java keywords are also known as reserved words. Keywords are particular words which acts as a key to a code. These are predefined words by Java so it cannot be used as a variable or object name.

List of Java Keywords

1. abstract
2. continue
3. for
4. new
5. switch
6. assert
7. default
8. goto
9. package
10. synchronized
11. boolean
12. do
13. if
14. private
15. this
16. break
17. double
18. implements
19. protected
20. throw
21. byte
22. else
23. import
24. public
25. throws
26. case
27. enum
28. instanceof
29. return
30. transient
31. catch
32. extends
33. int
34. short
35. try
36. char
37. final
38. interface
39. static
40. void
41. class
42. finally
43. long
44. strictfp
45. volatile
46. const
47. float
48. native
49. super
50. while

 

Keyword  Description

1. abstract: Java abstract keyword is used to declare abstract class. Abstract class can provide the implementation of interface. It can have abstract and non-abstract methods.
2. boolean: Java boolean keyword is used to declare a variable as a boolean type. It can hold True and False values only.
3. break: Java break keyword is used to break loop or switch statement. It breaks the current flow of the program at specified condition.
4. byte: Java byte keyword is used to declare a variable that can hold an 8-bit data values.
5. case: Java case keyword is used to with the switch statements to mark blocks of text.
6. catch: Java catch keyword is used to catch the exceptions generated by try statements. It must be used after the try block only.
7. char: Java char keyword is used to declare a variable that can hold unsigned 16-bit Unicode characters
8. class: Java class keyword is used to declare a class.
9. continue: Java continue keyword is used to continue the loop. It continues the current flow of the program and skips the remaining code at the specified condition.
10. default: Java default keyword is used to specify the default block of code in a switch statement.
11. do: Java do keyword is used in control statement to declare a loop. It can iterate a part of the program several times.
12. double: Java double keyword is used to declare a variable that can hold a 64-bit floating-point numbers.
13. else: Java else keyword is used to indicate the alternative branches in an if statement.
14. enum: Java enum keyword is used to define a fixed set of constants. Enum constructors are always private or default.
15. extends: Java extends keyword is used to indicate that a class is derived from another class or interface.
16. final: Java final keyword is used to indicate that a variable holds a constant value. It is applied with a variable. It is used to restrict the user.
17. finally: Java finally keyword indicates a block of code in a try-catch structure. This block is always executed whether exception is handled or not.
18. float: Java float keyword is used to declare a variable that can hold a 32-bit floating-point number.
19. for: Java for keyword is used to start a for loop. It is used to execute a set of instructions/functions repeatedly when some conditions become true. If the number of iteration is fixed, it is recommended to use for loop.
20. if: Java if keyword tests the condition. It executes the if block if condition is true.
21. implements: Java implements keyword is used to implement an interface.
22. import: Java import keyword makes classes and interfaces available and accessible to the current source code.
23. instanceof: Java instanceof keyword is used to test whether the object is an instance of the specified class or implements an interface.
24. int: Java int keyword is used to declare a variable that can hold a 32-bit signed integer.
25. interface: Java interface keyword is used to declare an interface. It can have only abstract methods.
26. long: Java long keyword is used to declare a variable that can hold a 64-bit integer.
27. native: Java native keyword is used to specify that a method is implemented in native code using JNI (Java Native Interface).
28. new: Java new keyword is used to create new objects.
29. null: Java null keyword is used to indicate that a reference does not refer to anything. It removes the garbage value.
30. package: Java package keyword is used to declare a Java package that includes the classes.
31. private: Java private keyword is an access modifier. It is used to indicate that a method or variable may be accessed only in the class in which it is declared.
32. protected: Java protected keyword is an access modifier. It can be accessible within package and outside the package but through inheritance only. It can't be applied on the class.
33. public: Java public keyword is an access modifier. It is used to indicate that an item is accessible anywhere. It has the widest scope among all other modifiers.
34. return: Java return keyword is used to return from a method when its execution is complete.
35. short: Java short keyword is used to declare a variable that can hold a 16-bit integer.
36. static: Java static keyword is used to indicate that a variable or method is a class method. The static keyword in Java is used for memory management mainly.
37. strictfp: Java strictfp is used to restrict the floating-point calculations to ensure portability.
38. super: Java super keyword is a reference variable that is used to refer parent class object. It can be used to invoke immediate parent class method.
39. switch: The Java switch keyword contains a switch statement that executes code based on test value. The switch statement tests the equality of a variable against multiple values.
40. synchronized: Java synchronized keyword is used to specify the critical sections or methods in multithreaded code.
41. this: Java this keyword can be used to refer the current object in a method or constructor.
42. throw: The Java throw keyword is used to explicitly throw an exception. The throw keyword is mainly used to throw custom exception. It is followed by an instance.
43. throws: The Java throws keyword is used to declare an exception. Checked exception can be propagated with throws.
44. transient: Java transient keyword is used in serialization. If you define any data member as transient, it will not be serialized.
45. try: Java try keyword is used to start a block of code that will be tested for exceptions. The try block must be followed by either catch or finally block.
46. void: Java void keyword is used to specify that a method does not have a return value.
47. volatile: Java volatile keyword is used to indicate that a variable may change asynchronously.
48. while: Java while keyword is used to start a while loop. This loop iterates a part of the program several times. If the number of iteration is not fixed, it is recommended to use while loop.

  Here I am going to sharing some of the important and frequently asking Java keywords interview questions and answers. So before going to java interview, refresh your mind go through the following Java keywords interview questions and answers.

What is use of synchronized keyword?

• This keyword is used to prevent concurrency. Synchronized keyword can be applied to static/non-static methods or a block of code. Only one thread at a time can access synchronized methods and if there are multiple threads trying to access the same method then other threads have to wait for the execution of method by one thread. Synchronized keyword provides a lock on the object and thus prevents race condition.

Example

 public void synchronized method(){
          // TO DO Something
       } 
    public void synchronized static method(){
         // TO DO Something
    } 
    public void myMethod(){ 
       synchronized (this){ // synchronized keyword on block of code 
       } 
    }

What is a static variable?

• Static keyword can be used with the variables and methods but not with the class. Anything declared as static is related to class and not objects.

Static variable :Multiples objects of a class shares the same instance of a static variable. Example

public class Counter{ 

private static int count=0; 

private int nonStaticcount=0;
 
public void incrementCounter(){ 

count++; 

nonStaticcount++; 

} 
public int getCount(){ 

return count; 

} 

public int getNonStaticcount(){ 

return nonStaticcount; 

} 
 
public static void main(String args[]){ 
 
 Counter countObj1 = new Counter(); 

 Counter countObj2 = new Counter(); 

 countObj1.incrementCounter(); 

 countObj1.incrementCounter(); 

 System.out.println("Static count for Obj1: "+countObj1.getCount()); 

 System.out.println("NonStatic count for Obj1: "+countObj1.getNonStaticcount()); 

 System.out.println("Static count for Obj2: "+countObj2.getCount()) 

 System.out.println("NonStatic count for Obj2: "+countObj2.getNonStaticcount()) 

}

Output

Static count for Obj1: 2

NonStatic count for Obj1: 1

Static count for Obj2: 2

NonStatic count for Obj2: 1

In the above program obj1 and obj2 share the same instance of static variable count hence if the value is incremented by one object , the incremented value will be reflected across the other objects.

What is a static method?

• A method defined as static is called static method. A static method can be accessed without creating the objects. Just by using the Class name the method can be accessed.
• Static method can only access static variables and not local or global non-static variables.

public class Test{ 

public static void printMe(){ 

System.out.println("Hello World"); 

  } 
} 

public class MainClass{ 

public static void main(String args[]){ 

Test.printMe() 

 } 
} 

Output
Hello World

Also static method can call only static methods and not non static methods. But non-static methods can call static mehtods.

Why static methods cannot access non static variables or methods?

• A static method cannot access non static variables or methods because static methods can be accessed without instantiating the class, so if the class is not instantiated the variables are not intialized and thus cannot be accessed from a static method.

What is static class ?

• A class cannot be declared static. But a class can be said a static class if all the variables and methods of the class are static and the constructor is private. Making the constructor private will prevent the class to be instantiated. So the only possibility to access is using Class name only

What is the use of final keyword?

The final keyword can be assigned to

1. Class level variable
2. method
3. Class
4. Objects

If a final is assigned to a variable, the variable behaves as a constant. It means that the value of variable once set cannot be changed.

final int i = 1; i = 5; // error  

If a final is assigned to a method then it cannot be overridden in its child class. Example

public class Parent { 
final void print(){ 
System.out.println("Inside"); 
} 
} 
 
public class Child extends Parent{ 
public final void print(){ 
// error cannot override final method 
System.out.println("Inside"); 
} 
}

If a class is made as final, then no other class can extend it and make it as parent class. Ex. String Class. Final objects are instantiated only once. i.e

final Map map = new HashMap(); map.put(“key”;,”value”); map = new HashMap(); // error  

What is throw keyword?

• Throw keyword is used to throw the exception manually. It is mainly used when the program fails to satisfy the given condition and it wants to warn the application.The exception thrown should be subclass of Throwable.

What is use of throws keyword?

• Throws clause is used to throw the exception from a method to the calling method which could decide to handle exception or throw to its calling method in a class.

What is a strictfp modifier?

• Strictfp is used with variable only .
• It is used to restrict floating point calculations ( fp ) to ensure portability ( platform Independent ). When this modifier is specified, the JVM adheres to the Java specifications ( IEEE-754 floating-point specification ) and returns the consistent value independent of the platform. That is, if you want the answers from your code (which uses floating point values) to be consistent in all platforms, then you need to specify the strictfp modifier.