Java Keywords

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

Let’s know the list of Java Keywords. A list of Java keywords or reserved words are given below:

abstract:

This keyword is used to declare abstract class. Abstract class can provide the implementation of interface. It can have abstract and non-abstract methods.

boolean:

The Java boolean keyword is used to declare a variable as a boolean type. It can hold True and False values only.

break:

Java break keyword is used to break loop or switch statement. It breaks the current flow of the program at specified condition.

byte:

The byte keyword is used to declare a variable that can hold an 8-bit data values.

case:

The java case keyword is used to with the switch statements to mark blocks of text.

catch:

Java catch keyword is used to catch the exceptions generated by try statements. It must be used after the try block only.

char:

The char keyword is used to declare a variable that can hold unsigned 16-bit Unicode characters

class:

In Java, the class keyword is used to declare a class.

continue:

In Java, the 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.

default:

The default keyword in java is used to specify the default block of code in a switch statement.

do:

The Java do keyword is used in control statement to declare a loop. It can iterate a part of the program several times.

double:

The Java double keyword is used to declare a variable that can hold a 64-bit floating-point numbers.

else:

The default Java else keyword is used to indicate the alternative branches in an if statement.

enum:

The Java enum keyword is used to define a fixed set of constants. Enum constructors are always private or default.

extends:

The default Java extends keyword is used to indicate that a class is derived from another class or interface.

final: The default 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.

finally: The default Java finally keyword indicates a block of code in a try-catch structure. This block is always executed whether exception is handled or not.

float: The Java float keyword is used to declare a variable that can hold a 32-bit floating-point number.

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.

if: The default  Java if keyword tests the condition. It executes the if block if condition is true.

implements: The default Java implements keyword is used to implement an interface.

import: The Java import keyword makes classes and interfaces available and accessible to the current source code.

instanceof: The default Java instanceof keyword is used to test whether the object is an instance of the specified class or implements an interface.

int: The default Java int keyword is used to declare a variable that can hold a 32-bit signed integer.

interface:

The default Java interface keyword is used to declare an interface. It can have only abstract methods.
long: The default Java long keyword is used to declare a variable that can hold a 64-bit integer.
native: The default Java native keyword is used to specify that a method is implemented in native code using JNI (Java Native Interface).

new: The default Java new keyword is used to create new objects.

null:

The default Java null keyword is used to indicate that a reference does not refer to anything. It removes the garbage value.

package:

The default Java package keyword is used to declare a Java package that includes the classes.

private:

The default 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.

protected:

The default 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.

public:

The default 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.

return:

The default Java return keyword is used to return from a method when its execution is complete.

short:

The default Java short keyword is used to declare a variable that can hold a 16-bit integer.

static:

The default 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.

strictfp:

The default Java strictfp is used to restrict the floating-point calculations to ensure portability.

super:

The default 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.

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.

synchronized:

Java synchronized keyword is used to specify the critical sections or methods in multithreaded code.

this:

In Java this keyword can be used to refer the current object in a method or constructor.

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.

throws:

The Java throws keyword is used to declare an exception. Checked exception can be propagated with throws.

transient:

In Java transient keyword is used in serialization. If you define any data member as transient, it will not be serialized.

try:

In 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.

void:

In Java void keyword is used to specify that a method does not have a return value.

volatile:

In Java volatile keyword is used to indicate that a variable may change asynchronously.

while:

In 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 is a few example with keywords:

public abstract class AbstractClass {
// This method is abstract ; it does not have a body
public abstract void abstractMethod();

// it is implemented in the abstract class and gives a default behavior.
public void concreteMethod() {
System.out.println("Already coded.");
}
}

The above code abstract keyword use here first method has no body as it is a abstract.

AbstractClass myObject = new AbstractClass() {
public void abstractMethod() {
System.out.println("Implementation.");
}
};

Above example code uses keyword new and the code has implemented method which has body.