5. Variables, Data Types and Escape Sequences in Java

 

Variables

• A variable is a container that stores a value.
• A variable is a name of the memory location and used to store data.
• Its value can be changed and it can be reused many times.

Rules for defining Variables

• A variable can have alphabets, digits and underscore.
  Mahi_7 is a valid variable name.
• A variable name can start with the alphabet, and underscore only. It can't start with a digit.
  7_Mahi is an invalid variable name.
• No whitespace is allowed within the variable name.
  MS Dhoni is an invalid variable name.
• Variable name is case sensitive.
  Mahi and mahi are different valid variable names.
• A variable name must not be any reserved word or keyword.
  void is a reserved word, so it is an invalid variable name.

Types of Variables

There are three types of variables in Java:

1. Local variable
2. Instance variable
3. Static variable

1. Local Variable

• A variable declared inside a function is called local variable.
• Local variable is accessible only within that function.
• Local variables are inaccessible to the functions of even same class outside the function they are declared in.

class Local {

    int method() {

        int m = 10;

        return m;

    }

    public static void main(String[] arr) {

        Local obj = new Local();

        System.out.println(obj.method());

    }

}

Output :

10

2. Instance Variable

• A variable declared inside the class but outside the body of the method.
• It value is instance specific and is not shared among instances.
• Their values are unique to each instance of a class.

class Instance {

    int m = 10;

    public static void main(String[] arr) {

        Instance obj = new Instance();

        System.out.println(obj.m);

    }

}

Output :

10

3. Static Variable

• A variable that is declared with the static keyword is called a static variable.
• We can create a single copy of the static variable and share it among all the instances of the class.
• Memory allocation for static variables happens only once when the class is loaded in the memory.
• Static variables can be accessed by calling with the class name.

class Static {

    static int m = 10;

    public static void main(String[] arr) {

        System.out.println(Static.m);

    }

}

Output :

10

Data Types

A data type specifies the type of data that a variable can store such as integer, float, character etc.

Boolean Data Type

• The Boolean data type is used to store only two possible values: true and false.
• Default value is false.
• The Boolean data type specifies one bit of information, but its size can't be defined precisely.

Byte Data Type

• It is an 8-bit (1 byte) signed two's complement integer.
• Its minimum value is -128, maximum value is 127 and default value is 0.
• The byte data type is used to save memory in large arrays and can also be used in place of int data type.

Short Data Type

• The short data type is a 16-bit (2 bytes) signed two's complement integer.
• Its minimum value is -32768, maximum value is 32767 and default value is 0.
• The short data type can also be used to save memory just like byte data type.

Int Data Type

• The int data type is a 32-bit (4 bytes) signed two's complement integer.
• Its minimum value is -2147483648, maximum value is 2147483647 and default value is 0.
• The int data type is generally used as a default data type for integral values unless if there is no problem about memory.

Long Data Type

• The long data type is a 64-bit (8 bytes) two's complement integer.
• Its minimum value is -9223372036854775808, maximum value is 9223372036854775807 and default value is 0.
• The long data type is used when we need a range of values more than those provided by int.

Float Data Type

• The float data type is a single precision 32-bit (4 bytes) floating point.
• Its value range is unlimited and default value is 0.0f.
• It is recommended to use a float (instead of double) to save memory in large arrays of floating point numbers.

Double Data Type

• The double data type is a double-precision 64-bit (8 bytes) floating point.
• Its value range is unlimited and default value is 0.0d.
• The double data type is generally used for decimal values just like float.

Char Data Type

• The char data type is a single 16-bit Unicode character.
• Its minimum value is '\u0000' or 0, maximum value is '\uffff' or 65535 and default value is '\u0000'.
• The char data type is used to store characters.

Program to display size of Data Types

class Size {

    public static void main(String[] arr) {

        System.out.println("Size of byte: " + (Byte.SIZE / 8) + " bytes");

        System.out.println("Size of short: " + (Short.SIZE / 8) + " bytes");

        System.out.println("Size of int: " + (Integer.SIZE / 8) + " bytes");

        System.out.println("Size of long: " + (Long.SIZE / 8) + " bytes");

        System.out.println("Size of float: " + (Float.SIZE / 8) + " bytes");

        System.out.println("Size of double: " + (Double.SIZE / 8) + " bytes");

        System.out.println("Size of char: " + (Character.SIZE / 8) + " bytes");

    }

}

Output :

Size of byte: 1 bytes
Size of short: 2 bytes
Size of int: 4 bytes
Size of long: 8 bytes
Size of float: 4 bytes
Size of double: 8 bytes
Size of char: 2 bytes

Escape Sequences in Java

An escape sequence in Java language is a sequence of characters that doesn't represent itself when used inside string literal or character.
It is composed of two or more characters starting with backslash \. For example : \n represents a new line.

List of Escape Sequences in Java

Escape Sequences	Meaning
\t	Insert a tab in the text at this point.
\b	Insert a backspace in the text at this point.
\n	Insert a newline in the text at this point.
\'	Insert a single quote character in the text at this point.
\"	Insert a double quote character in the text at this point.
\\	Insert a backslash character in the text at this point.

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