Java Data Type Tutorial - Java Data Type

The following two lines Java code defines two integers, num1 and num2:

int num1;
int num2;

num1 and num2 are two int variables.

The int keyword indicates that the name that follows represents an integer value, for example, 10, 15, 70, 1000, etc.

Because you have declared num1 and num2 variables of int data type, we cannot store a real number, such as 10.1.

The following piece of code stores 5 in num1 and 7 in num2:

num1 = 5;
num2 = 7;

Two kinds of data types

Java supports two kinds of data types:

  • Primitive data type
  • Reference data type

A variable of the primitive data type holds a value whereas a variable of the reference data type holds the reference to an object in memory.

String is a class defined in the Java library and we can use it to manipulate sequence of characters.

You declare a reference variable str of String type as

String str;

There is a reference constant null, which can be assigned to any reference variable.

If null is assigned to a reference variable, it means that the reference variable is not referring to any object in memory.

The null reference literal can be assigned to str.

str = null;

A String object is created using the new operator.

Strings are used so often that there is a shortcut to create a string object.

All string literals, a sequence of characters enclosed in double quotes, are treated as String objects.

We can use string literals like so:

// Assigns "Hello" to str1
String str1 = "Hello";

// Assigns the   reference of  a  String object with  text  "Hello" to str1
String str1 = new String ("Hello");