Java Data Types

We know that 2 is an integer, ‘a’ is a character and “Let’s learn Java” is a sentence. All these values require different amounts of space in the memory. For example, the space required to store an integer is different from that required to store a character.

In all the examples in the previous chapter, the variables were declared of type int and thus can store only integer values. However, we can also declare variables which can store a character, a sentence or other types of values.

Variables can be of different types depending on the type of data it can store. A variable which stores an integer value is of type int. Similarly, a variable which stores a character value is of type char.

We specify the type of a variable at the time of its declaration. For example, a character variable is declared as shown below.

char ch;

In the above declaration, ch is the name of a variable which is of type char i.e., it can store only character values.

Most commonly used data types in Java are int (integer), char (character), float (number having decimal), double (number having decimal), String (collection of characters) and boolean (true or false).

Let’s look at these data types.

Data Types in Java

int

The int data type is used to store integers. Integers are numbers which don’t have decimal. For example, -5, 0, 6, etc.

class Test {

    public static void main(String[] args) {
        int num;
        num = 10;
        System.out.println(num);
    }
}

The variable num is declared of type int and is assigned an integer value 10.

double

The double data type is used to store double-precision 64-bit floating point numbers. Floating point numbers are numbers which have decimal. In other words, the double data type is used to store numbers having decimal. For example, -5.64, 10.228, etc.

class Test {

    public static void main(String[] args) {
        double num;
        num = 10.5;
        System.out.println(num);
    }
}

The variable num is declared of type double and is assigned a floating point value 10.5.

float

The float data type is used to store single-precision 32-bit floating point numbers. A float value should always end with f or F. For example, -5.64f, 10.228F, etc.

class Test {

    public static void main(String[] args) {
        float num;
        num = 10.5f;
        System.out.println(num);
    }
}

In this example, we assigned the value 10.5f and not 10.5 to the variable num because 10.5 is a double. To tell the compiler to consider 10.5 as a float, we assigned 10.5f to the variable.

char

The char data type is used to store a character. A character value must be written within single quotes ' '. For example, ‘a’, ‘B’, ‘@’, etc.

class Test {

    public static void main(String[] args) {
        char ch;
        ch = 'e';
        System.out.println(ch);
    }
}

Here, ch is the name of a variable of type char which is assigned a character value 'e'.

String

The String data type is used to store a string. A string is a sequence of characters. For example, “Hello” is a string having characters ‘H’, ‘e’, ‘l’, ‘l’ and ‘o’.

A string value must be enclosed within double quotes " ". In fact, any value enclosed within double quotes " " is a string. Some examples of string are “Hello World”, “Hello123”, "123" and “Name: John”.

class Test {

    public static void main(String[] args) {
        String msg;
        msg = "Let's learn Java";
        System.out.println(msg);
    }
}

In this example, the variable msg is declared of type String and is assigned the string "Let's learn Java".

As we know that any value enclosed within double quotes “ “ is a string, so values like “10” and “10+2” are also strings.

Look at the following example.

class Test {

    public static void main(String[] args) {
        int a = 10 + 2;
        String b = "10 + 2";
        System.out.println(a);
        System.out.println(b);
    }
}

In the above example, the integer variable a is assigned the expression 10 + 2. This expression first gets evaluated to 12 and then 12 is assigned to a. On the other hand, the string variable b is assigned the string "10 + 2".

We will learn more about String later in the topic Strings.

boolean

The boolean data type consists of two values - true and false.

class Test {

    public static void main(String[] args) {
        boolean a, b;
        a = true;
        b = false;
        System.out.println(a);
        System.out.println(b);
    }
}

The variables a and b are declared of type boolean and are assigned the values true and false respectively.

So these were all the basic data types. Now, let’s look at the range of values that different data types can take.

The following table states different data types along with the maximum and minimum value they can take.

Let's see an example of double, char and boolean values.

class Test {

    public static void main(String[] args) {
        double b = 123.43555;
        char c = 'e';
        boolean d = true;
        System.out.println("Double: " + b);
        System.out.println("Character: " + c);
        System.out.println("Boolean: " + d);
    }
}

You must have understood the code. While printing, + joined a string and the value of a variable in each System.out.println() method.

In the first System.out.println() method, the string "Double: " and the value of b (because b is not inside " ") are combined and printed.

Look at another example.

class Test {

    public static void main(String[] args) {
        int x = 1, y = 5;
        System.out.println("x");
        System.out.println("y");
        System.out.println("x" + "y");
        System.out.println(x);
        System.out.println(y);
        System.out.println(x + y);
    }
}

Here, whatever is written within " " got printed as it is, without getting evaluated. Whatever is not inside " " got evaluated first and then their values got printed. For example, "x"+"y" got printed as xy (without evaluation) but x+y got evaluated first as 1+5 i.e., 6 and then 6 got printed.

Primitive and Non-Primitive Data types

Using data types is so easy, isn't it?

All the data types are broadly classified into primitive and non-primitive.

Primitive Data type

Primitive data types are predefined (already defined) data types in Java.

There are eight predefined data types in Java, which are

int, float, double, short, long, char, boolean, byte

Non-Primitive Data type

Non-primitive data types are defined by the programmer. Some examples of non-primitive data types are Array, Class and Interface.

At present, there is no need to go into the details of non-primitive data types as we will learn about them later.

Type Casting

Suppose we are writing a program and we have an integer variable having a value 10 (an integer) and at some point of time we want it to be a string i.e., “10”. Or a more practical case would be to convert a double (10.2) to an integer (10). We can easily do so in Java using type casting.

Type Casting is the conversion of a value from one data type to another data type. For example, we can convert a double value to an int value or a char value to an int value.

Type Conversions are of two types - implicit and explicit.

Implicit Conversion

Suppose we are adding two numbers. The first number is of type int and the second number is of type double. We cannot add an int and a double because both the numbers have to be of the same data type i.e. either both are int or both are double. Since double is a larger data type than int, therefore while adding, the int variable automatically gets converted into double and then both the double variables add up.

From the above order, we can see that double is the largest data type and short is the smallest data type. Any smaller data type gets implicitly converted into a larger data type when performing arithmetic operations or in any such other expression.

For example, when adding a value of type int and a value of type long, the value of type int gets automatically converted to long and then both the values get added.

Similarly, a char variable gets converted into an int while performing some arithmetic operation.

class Test {

    public static void main(String[] args) {
        int n = 10;
        char ch = 'h';
        int sum = n + ch;
        System.out.println(sum);
    }
}

In the above program, when the variables n and ch are added, the integer value (ASCII value) of ch i.e. 104 is added to the value of n to produce a sum of 114. Note that every character has an ASCII value. You can get the ASCII chart from here.

Explicit Conversion

We know that a smaller data type can be implicitly converted to a larger data type. But what if we want to convert a larger data type to a smaller data type?

We can also convert values from one data type to another as shown below:

( data-type ) expression;

For example, a double value 10.5 can be converted to int as shown below.

(int)10.5;

Consider an example.

class D3 {

    public static void main(String[] args) {
        int sum = 23;
        int n = 7;
        double avg;
        avg = (double) sum / n;
        System.out.println("Average = " + avg);
    }
}

In this example, since the variable avg is declared of type double, we are converting sum/n to type double by writing (double)sum/n (since int/int gives int in Java).

You will understand many concepts only by practicing. So, solve questions from the practice section.