Data Type

• A data type is a classification of data.
• It represents the type and size of data values that can be stored in a variable.
• In other words, a Java data type is a set of values and operations defined on those values.

Data types are divided into two groups:

1. Primitive data type
2. Non-primitive data type

Primitive Data Type

Primitive data types are basic data types that specify the size and type of data and cannot be further divided into simpler data types.

1. Integer Types

It stores whole numbers, positive and negative, without decimals. Valid types are byte, short, int and long.

2. Floating Point Types

It stores numbers with a fractional part containing one or more decimals. Two types are float and double.

3. Character Type

• The char data type is used to store a single character.
• It occupies 2 bytes of memory.
• The character value must be surrounded by single quotes, like 'A' or 'a'.

4. Boolean Type

• The boolean data type is used to store a logical value, either true or false.
• It occupies 1 bit memory space.

String Type

The String type is used to store a sequence of characters (text). String value must be surrounded by double quotes, like "Ram".

Example

String name = "RAM";
System.out.println(name);

Variables

• Variables are containers for storing data values.
• They are names of memory locations that store different types of data specified by data types.

Declaration of Variable

Syntax:

datatype variableName = value;

Examples

int num = 5;
float marks = 45.5f;
char grade = 'A';
boolean mybool = true;
String name = "Bipana";

Program to Add Numbers

class sum
{
    public static void main(String []args)
    {
        int a = 5;
        int b = 6;
        int sum = a + b;

        System.out.println("The sum =" + sum);
    }
}

Constant

Constant is a value that cannot be changed after assigning it.

Java does not support the constant directly.

There is an alternative way to define constant in Java using non-access modifiers static and final.

Static and Final Modifiers

static modifier: It is used to manage memory. It allows the variable without loading any instance of the class in which it is defined.

final modifier: It represents that the value of the variable cannot be changed. It also makes primitive data types immutable.

Syntax for Creating Constants

static final type identifier_name = value;

// Example
static final double pi = 3.1416;

Identifier

• Identifiers are symbolic names used for identification.
• They can be class name, variable name, method name, package name, constant name and more. These unique names are called identifiers.

Rules for Naming Identifiers

1. Valid identifiers must have characters A–Z or a–z, numbers 0–9 and underscore (_).
2. Should not start with a number.
3. Should not have a space in an identifier.
4. The source says: “Should be length 4–15 letter only. However there is not limit on its length.”
5. Keywords cannot be used as identifiers.
6. The source states that Oracle-language keywords such as SELECT, FROM, WHERE, DELETE, etc. cannot be identifiers.
7. Identifiers are case sensitive.

Some Valid Identifiers

a
Sum
num1
num_1
pi
CalculateArea1
RectArea

Keywords

Java keywords are predefined or reserved words used for functionality or meaning.

Keywords cannot be used for identifiers.

List of Java Keywords Shown in the Scan

Access Modifiers

The access modifier specifies the accessibility or scope of a field, method, class or constructor.

Access level can be changed by applying the access modifier on a field, method, class or constructor.

4 Types of Java Access Modifiers

1. Private
2. Default
3. Protected
4. Public

1. Private

The access level of private modifier is only within the class. It cannot be accessed from outside of the class.

2. Default

The access level of default modifier is only within the package. It cannot be accessed from outside the package.

3. Protected

The access level is within package and outside the package through child class. If we do not make a child class, it cannot be accessed from outside the package.

4. Public

The access level of it is anywhere. It can be accessed from within the class, outside the class, within the package and outside the package.

Example of Private Access Modifier

class A
{
    private int data = 40;

    private void msg()
    {
        System.out.println("Hello Java");
    }
}

public class Test
{
    public static void main(String []args)
    {
        A obj = new A();

        System.out.println(obj.data);
        obj.msg();
    }
}

Escape Sequence in Java

A character preceded by a backslash (\) is an escape sequence and has a special meaning to the compiler.

Types of Escape Sequences in Java

Operators in Java

• Operators are special symbols that perform certain operations on operands.
• They are used to perform operations on variables and values.

In Java, operators are divided into the following categories in the scan:

1. Arithmetic operator
2. Assignment operator
3. Logical operator
4. Relational operator
5. Bitwise operator
6. Unary operator
7. Ternary operator

1. Arithmetic Operator

Used to perform basic arithmetic operations such as addition, subtraction, etc.

Example

public class OperatorTest
{
    public static void main(String []args)
    {
        int a = 20;
        int b = 5;

        System.out.println(a + b);
        System.out.println(a - b);
        System.out.println(a * b);
        System.out.println(a / b);
        System.out.println(a % b);
    }
}

2. Assignment Operator

Assignment operators are used to assign/store the value of the right-hand operand to the left-hand operand or variable.

3. Logical Operator

Logical operators are used to combine two or more conditions.

They return a logical value either true or false.

4. Relational Operators

Relational operators are used to check the relationship between two operands.

If the relationship (condition) is true, it returns true value; otherwise it returns false value.

Example

public class RelationalOP
{
    public static void main(String []args)
    {
        int a = 10, b = 5;

        System.out.println(a == b);
        System.out.println(a > b);
        System.out.println(a >= b);
        System.out.println(a < b);
        System.out.println(a <= b);
        System.out.println(a != b);
    }
}

5. Bitwise Operators

These operators are used to perform bit-level operations on integer and boolean data.

Program Example

public class BitwiseOP
{
    public static void main(String []args)
    {
        int A = 10, B = 3;

        System.out.println(A & B);
        System.out.println(A | B);
        System.out.println(A ^ B);
        System.out.println(~A);
        System.out.println(A << 2);
        System.out.println(A >> 2);
    }
}

Bitwise Left Shift (a << 2)

Bitwise Right Shift (a >> 2)

6. Unary Operators

• It takes only a single operand.
• Used to increment or decrement the value, negate an expression or invert a boolean value.

I. Increment Operator (++)

Used to increment the value of operand by 1.

Two types: post-increment (a++) and pre-increment (++a).

In post-increment, the value is first used for computing the result and then incremented.

In pre-increment, the value is incremented first and then the result is computed.

II. Decrement Operator (--)

Used for decrementing the value of operand by 1.

Also two types: post-decrement (a--) and pre-decrement (--a).

III. Logical NOT Operator (!)

Used for inverting a boolean value (!b).

Sample Example

public class OpTest
{
    public static void main(String []args)
    {
        int a = 10;
        boolean b = true;

        System.out.println(a++);
        System.out.println(++a);
        System.out.println(a--);
        System.out.println(--a);
        System.out.println(!b);
    }
}

Result Notes Written in the Scan

7. Ternary Operator

• It is a shorthand version of the if-else statement.
• It has 3 operands and hence the name ternary.

General Format

(condition ? true-value : false-value)

If condition is true, then execute the statement after ?; else execute the statement after :.

Sample Example

public class OPTest
{
    public static void main(String []args)
    {
        int a = 20, b = 10;
        int result;

        result = ((a > b) ? a : b);

        System.out.println("greater no is = " + result);
    }
}

8. If / Else Structure

The last scanned page shows the following if/else structure:

if (condition)
{
    statement 1;
}
else
{
    statement 2;
}