Data Types in Java

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• Java is rich in its data type.

• Data type tells the type of data, that you are going to store in memory.

• It gives the information that which operations that may be performed on it.

In Java there are two types of data types:
     1 . Primitive data types
     2 . Non-primitive data types

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Primitive Data Types

• The Java programming language supports eight primitive data types.

• A primitive type is predefined by the language and is named by a reserved keyword.

• Primitive values do not share state with other primitive values.

The eight primitive data types supported by the Java programming language are:

public class DefaultValuesTest{
    //(instance/non-static variable) primitive data type
    byte b; 
    short sh;
    int a;
    long l;
    float f;
    double d;
    char ch;
    boolean bool;
    
    // (class/static variable) primitive data type
    static int x;
    
    // class type (reference variable)
    String s;
    
    void showValues(){
        System.out.println("Default Value of bye, b is :"+b);
        System.out.println("Default Value of short, sh is :"+sh);
        System.out.println("Default Value of int, a is :"+a);
        System.out.println("Default Value of long, l is :"+l);
        System.out.println("Default Value of float, f is :"+f);
        System.out.println("Default Value of double, d is :"+d);
        System.out.println("Default Value of char, ch is :"+ch);
        System.out.println("Default Value of boolean, bool is :"+bool);
        System.out.println("Default Value of static int, x is :"+x);
        System.out.println("Default Value of non-primitive String, s is :"+s);
    }
    
    public static void main(String [] args){
        DefaultValuesTest ob = new DefaultValuesTest();
        ob.showValues();
        
    }
}

OUTPUT

Default Value of bye, b is :0
Default Value of short, sh is :0
Default Value of int, a is :0
Default Value of long, l is :0
Default Value of float, f is :0.0
Default Value of double, d is :0.0
Default Value of char, ch is :
Default Value of boolean, bool is :false
Default Value of static int, x is :0
Default Value of non-primitive String, s is :null                                    
                                

Tips :

1. There are only two values for boolean data type either true or false, and cannot replace it with 1 or 0.

2. Default values are for fields, not for local variables.

3. The compiler never assigns a default value to an uninitialized local variable. make sure to assign it a value before you attempt to use it.

LocalDefaultValueTest.java Copy Code

public class LocalDefaultValueTest{
    
    public static void main(String [] args){
        int x; // local varaible
        System.out.println("Value of local variable x :"+x);
        
    }
}

OUTPUT

LocalDefaultValueTest.java:5: error: variable x might not have been initialized
        System.out.println("Value of local variable x :"+x);
                                                         ^
1 error

4. Accessing an uninitialized local variable will result in a compile-time error.

5. Default value for reference variable is null.

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