Java simple programs

This tutorial contains basic programs like sum, average, circle and rectangle area etc in java. The tutorial also covers some key concepts about variables and data types, let's see the basic programs first followed by the key concepts.

The program below shows how to add two number and also shows how to find average of two number. Similarly you can develop your own program to add multiple numbers or find the average of multiple numbers.

Addition program in java | Average program in java

 class AdditionAndAverage  {
    public static void main(String [] args) {          
        int firstNum = 1234;  
        int secondNum = 5678;  
        int sum = firstNum + secondNum; // Adding two number
        int avg = (firstNum + secondNum)/2; // Calculating average of two number
        System.out.println("sum = "+sum);
        System.out.println("Average = "+avg);                  
     }
 }

Output:

sum = 6912
Average = 3456

The program below shows how to multiply and divide two numbers in java. Be careful to use the correct data type for storing the result of these operations. For example if division of two number results as a decimal(eg. 20.25, 245.3 etc) type value, then store it in any of the float(float, double) data types.

Multiplication program in java | Java division program

 class MultiplicationAndDivision {
    public static void main(String [] args) {          
        int firstNum = 100;  
        int secondNum = 5;  
        int result = firstNum * secondNum; // Multiplying two number
        int result2 = firstNum / secondNum; // Dividing two number
        double result3 = (double)200 / 6; // Division which returns decimal type value
        System.out.println("multiplication = "+result);
        System.out.println("Division = "+result2);      
        System.out.println("result3 = "+result3);                  
    }
 }

Output:

multiplication = 500
Division = 20
result3 = 33.333333333333336

Program below shows how to find area of a circle for given radius and area of rectangle for given length and width.

Area of circle java program | Area of rectangle java program

 class CalculateArea {
    public static void main(String [] args) {          
        float radius = 10.5f; 
        float pi = 22/7f; 
        int length = 10;  
        int width = 20;
        float circleArea = pi*radius*radius; // Calculating area of circle
        int rectArea = length*width; // Calculating area of rectangle
        System.out.println("area of circle = "+circleArea);
        System.out.println("area of rectangle = "+rectArea);                  
    }
 }

Output:

area of circle = 346.5
area of rectangle = 200

Some key points about variables & data types

Following are some of the key points that we should be aware of :

By default, operations on integer variables (eg 5+15, 2+3*5) returns an int type value, if result needs to be assigned into any other integer data type(eg. byte or short) variable, it must be casted explicitly.
The value in a char variable must be a single character, assigning multiple character will result in compilation error.
A boolean variable value must be given as true or false. it should not be like 'true',"true", "false" etc.

What do \n and \t do in java program ?

The \n and \t are part of escape sequence characters in java. In java \n is used to insert a newline in the text at this point which means anything that you write after \n in a string that will be printed in a new line. While \t is used to insert a tab in the text at this point which means anything written after \t in a string will be printed after a tab space. Refer the program below.

Along with \n and \t there are several more escape sequence characters in java, you can refer this link to get details about them. Let's see all above points in the program below :

Java program of \n and \t escape character

 class VariableAndDataType  {
    public static void main(String [] args)  {          
        byte a = 20;  
        byte b = 10;  
        byte sum = (byte)(a+b); // casting explicitly
        // char ch = 'abc'; // Can not assign multiple characters
        char ch = 'a';         
        // boolean b2 = 'false' , c ="false";  // Can not use '', or ""
        boolean b2 = false;
        System.out.println("sum = " +sum); 
        System.out.println("ch = " +ch); 
        System.out.println("b2 = "+ b2);  
        System.out.println("First line \nSecond line");
        System.out.println("refresh \t java");
        System.out.println("Displaying \" in string.");                  
      }
   }

Output:

sum = 30
ch = a
b2 = false
First line
Second line
refresh java
Displaying " in string.

Let's see few more points that we should be aware of while writing the program in java :

If an integer value is assigned to any float data types, java will automatically convert that integer number to float number by appending .0 in value of that variable.
Values of integer data types can be given in three different number system - Decimal, HexaDecimal and Binary. Binary number system is supported from java SE 7 and above. HexaDecimal values are given with a prefix 0x while binary values are prefixed with 0b.

Java hexaDecimal program | Java binary representation program

 class VariableAndDataTypeExample {
    public static void main(String [] args) {          
        float f = 15;  
        byte b = 125;  
        double d = b;
        int hexVal = 0x18; // Hexadecimal representation
        int binVal = 0b101010; // Binary representation
        System.out.println("f = " +f); 
        System.out.println("d = " +d); 
        System.out.println("hexVal = " +hexVal); // Prints the decimal value of hexVal variable 
        System.out.println("binVal = " +binVal); // Prints the decimal value of binVar variable              
      }
   }

Output:

f = 15.0
d = 125.0
hexVal = 24
binVal = 42

How are hexadecimal numbers represented in Java ?

Hexadecimal numbers are represented via a prefix 0x. If a number starts with 0x, it means it's a hexadecimal number. So anything after 0x is considered as hexadecimal number. For example in assignment int val = 0x18; 18 will be considered as hexadecimal number, in decimal it represents number 24. Refer the program example given above.

How are binary numbers represented in Java ?

Binary numbers are represented via a prefix 0b. If a number starts with 0b, it means it's a binary number. So anything after 0b is considered as binary number. For example in assignment int val = 0b101010; 101010 will be considered as binary number, in decimal it represents number 42. Refer the program example given above.

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