Data types in Java with examples

Data types in Java are used to know the type of variables. The variable can be of any type like numeric or non-numeric or boolean etc. Data types also help to assign a sufficient amount of memory to the variable.

Ex. int result = 50;

Explanation

The result is a numeric field as we have made use of the int data type.
The int data type will allocate 4 bytes of memory to the result variable

Types of data types

Java data types are classified into 3 types:

1. Primitive or Built-In or Predefined data types
2. Derived data types
3. Non Primitive or User-defined data types

Predefined data types

These are developed by programming language developers. Java developers have created java data types for us. Predefined data types are provided to us by default. We just have to make use of them. Predefined data types allow us to store only a single value it does not allow us to store multiple values.

Java provides 8 predefined data types which are categorized into 4 categories :

1. Integer category data type
2. Float category data type
3. Character category data type
4. Boolean category data type

Integer category data type

This data type allocates sufficient memory for integer data in the main memory of the computer. The integer data type contains numeric data without decimals.

Integer category contains 4 subtypes:

byte – This data type allocates 1 byte of memory to the variable.

Range = -127 to 128

short – This data type allocates 2 bytes of memory to the variable.

Range = -32,768 to 32,767

int – This data type allocates 4 bytes of memory to the variable.

Range = -2,147,483,648 to 2,147,483,647

long – This data type allocates 8 bytes of memory to the variable.

Range = -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

Calculating range

Formula : (-2^n) to (2^n – 1)

byte : 8 bits

n = 8-1 = 7

= -2^7 to (2^7) – 1
= -128 to 127

int : 32 bits 

n = 32-1 = 31

= -2^31 to (2^31) – 1
= -2,147,483,648 to 2,147,483,647

As a developer we have to choose appropriate data type. 

Ex. byte b = 128; // This will throw an exception because the range of byte is from -128 to 127

Float category data type

This category of data type allocates sufficient memory for real constant numbers in the main memory of the computer. Float data type contains numeric data with decimals.

The float category contains 2 subtypes:

float – float data type allocates 4 bytes of memory to the variable. float data type stores the value in such a way that after the dot(.) it takes 7 decimal places. float value should end with the letter f else we will get compile time error.

Range [ 3.4e−038 to 3.4e+038 ]

Ex. float f = 2.5f;

double – double data type allocates 8 bytes of memory to the variable. double data type stores the value in such a way that after the dot(.) it takes 15 decimal places. double value may end or may not end with the letter d, it is optional.

Range [ 1.7e−308 to 1.7e+308 ]

Ex. double d = 2.5 or double d = 2.5d;

Note* If we use any real constant value in our program then by default it will be double data type.

Character category data type

This category of data types allocates sufficient memory for single-character data. This category contains only one data type i.e. char.

char data type in java allocates 2 bytes of memory to the variable.

Ex. char ch = 'a';

Boolean category data type

This category contains only one data type i.e. boolean. The purpose of this data type is to store logical values i.e. true or false. This data type contains only 1 bit of information hence no size is defined for it.

Ex. boolean result = true;

Default values of predefined data types

When declaring a variable if we do not assign any value to the variable then JVM will provide some default values to that variable.

byte - default value is 0
short - default value is 0
int - default value is 0
long - default value is 0
float - default value is 0.0
double - default value is 0.0
char - default value is \u0000' (nothing that is equivalent to null)
boolean - default value is false

Below is the sample program to display the default values of predefined data types

package com.javahandson;

public class DefaultValues {

    byte b;
    short s;
    int i;
    long l;

    float f;
    double d;

    char ch;
    boolean bool;

    public static void main(String[] args) {

        DefaultValues defaultValues = new DefaultValues();

        System.out.println("byte default value is : "+defaultValues.b);
        System.out.println("short default value is : "+defaultValues.s);
        System.out.println("int default value is : "+defaultValues.i);
        System.out.println("long default value is : "+defaultValues.l);

        System.out.println("float default value is : "+defaultValues.f);
        System.out.println("double default value is : "+defaultValues.d);

        System.out.println("char default value is : "+defaultValues.ch);
        System.out.println("boolean default value is : "+defaultValues.bool);
    }
}

Output :

byte default value is : 0
short default value is : 0
int default value is : 0
long default value is : 0
float default value is : 0.0
double default value is : 0.0
char default value is :  
boolean default value is : false

Derived data types

The derived data type is composed of primitive data types. Derived data types include Arrays, Pointers, Structures, Union etc. Pointers are not supported by Java also Java has no complex data types like structures or unions. So for Java, we are left with Arrays.

Array helps us to store multiple values of the same data type in a single variable. It is also known as a homogeneous data structure as it contains only homogeneous data.

int[] arr = {20, 30, 70, 80}; // Valid as it only contains integer values.

int[] arr = {20, "Java", 70, true}; // Invalid as it contains string as well as boolean values.

User-defined data types

These are the data types created by a user or a developer. User-defined data types allow us to store multiple values of the same data types or different data types. In Java, we can use features like Class, Interface or Enumeration to create user-defined data types.

Below is the sample program to show a user-defined data type i.e class

package com.javahandson.oops;

public class Student {

    int studentId;
    String name;
    String standard;

    public int getStudentId() {
        return studentId;
    }

    public void setStudentId(int studentId) {
        this.studentId = studentId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getStandard() {
        return standard;
    }

    public void setStandard(String standard) {
        this.standard = standard;
    }
}

Note* The string data type is a non-primitive data type but it is also predefined in Java. A string data type is used to store the sequence of characters.