Java

Programming Fundamentals · Wikibooks

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    From Wikibooks, under CC BY-SA 4.0, as the source states it. This page at Wikibooks.

    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