< Programming Fundamentals

Overview

The following examples demonstrate data types, arithmetic operations, and input in Java.

Data Types

// This program demonstrates variables, literal constants, and data types.

public class Main {
    public static void main(String[] args) {
        int i;
        double d;
        String s;
        boolean b;
        
        i = 1234567890;
        d = 1.23456789012345;
        s = "string";
        b = true;

        System.out.println("Integer i = " + i);
        System.out.println("Double d = " + d);
        System.out.println("String s = " + s);
        System.out.println("Boolean b = " + b);
    }
}

Output

Integer i = 1234567890
Double d = 1.23456789012345
String s = string
Boolean b = true

Discussion

Each code element represents:

  • // begins a comment
  • public class DataTypes begins the Data Types program
  • { begins a block of code
  • public static void main(String[] args) begins the main function
  • int i defines an integer variable named i
  • ; ends each line of Java code
  • double d defines a double floating-point variable named d
  • string s defines a string variable named s
  • boolean b defines a Boolean variable named b
  • i = , d = , s =, b = assign literal values to the corresponding variables
  • System.out.println calls the  standard output print line function
  • } ends a block of code

Arithmetic

// This program demonstrates arithmetic operations.

public class Main {
    public static void main(String[] args) {
        int a;
        int b;
        
        a = 3;
        b = 2;

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

Output

a = 3
b = 2
a + b = 5
a - b = 1
a * b = 6
a / b = 1
a % b = 1

Discussion

Each new code element represents:

  • +, -, *, /, and % represent addition, subtraction, multiplication, division, and modulus, respectively.

Temperature

// This program converts an input Fahrenheit temperature to Celsius.

import java.util.*;

public class Main {
    private static Scanner input = new Scanner(System.in);

    public static void main(String[] args) {
        double fahrenheit;
        double celsius;
        
        System.out.println("Enter Fahrenheit temperature:");
        fahrenheit = input.nextDouble();

        celsius = (fahrenheit - 32) * 5 / 9;
        
        System.out.println(Double.toString(fahrenheit) + "° Fahrenheit is " + celsius + "° Celsius");
    }
}

Output

Enter Fahrenheit temperature:
 100
100° Fahrenheit is 37.7777777777778° Celsius

Discussion

Each new code element represents:

  • private static Scanner input ... defines an object to read from standard input
  • input.nextDouble() reads input as a double floating-point value

References

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