Data Types, thesarfo

There are 2 types of datatype in Java: primitive and reference types.

Primitive data types

Primitives store values — for instance int is a primitive type, and it stores integer values. In Java, primitives come in different sizes, and those sizes have names. When you declare any variable in Java, you must declare it with a specific type. There are 8 primitive data types in Java, and 6 of them store different number types.

class HelloWorld {
    public static void main(String[] args) {
        // integer types
        byte aSingleByte = 100; // -128 to 127
        short aSmallNumber = 20000; // -32,768 to 32,767
        int anInteger = 2147483647; // -2147483648 to 2147483647
        long aLargeNumber = 9223372036854775807L;

        // decimal types
        double aDouble = 1.79769313; // 4.9E-324 to 1.7976931348...
        float aFloat = 3.4028F; // 1.4E-45 to 3.4028235E38

        // booleans
        boolean isWeekend = false;
        boolean isWeekday = true;

        // characters
        char copyrightSymbol = '©';
        char single = 'a';

        System.out.println(("This is the copyright symbol: " + copyrightSymbol));
    }
}

Usually for numbers, the int and double types should suffice for normal numbers and numbers that have decimal points respectively.

Reference types

They store the reference to a memory location where a dynamic object is being stored. An array is an example.

Type conversion

You can convert a variable to another datatype — for instance, we can convert an integer to a double. There are implicit and explicit type conversions: with implicit, the compiler does it for us; with explicit, we have to explicitly tell the compiler that we want to perform a type conversion.

class Main {
    public static void main(String[] args) {
        // implicit type conversion, the compiler does it for us
        int number1 = 5;
        double number2 = number1;

        System.out.println(number2); // outputs 5.0 i.e. a double
    }
}

But conversion from a double to an int is not possible unless we do that ourselves.

class Main {
    public static void main(String[] args) {
        // explicit type conversion
        double number1 = 5.8;
        int number2 = (int) number1; // the (int) tells the compiler we want to convert number1 into an int and store it in number2

        System.out.println(number2); // outputs 5
    }
}