Simple Java Programs : Basic Fundamentals for Beginners
Java is a high-level object oriented programming language and some users may find it tough. However, these sets of programs will make you comfortable with the Java programming language and its basic concepts. You will see a set of programs mentioned below that ranges from a simple “hello world” application to searching for a number. It covers all the small details that every beginner must know to be a Java programmer.
Program to Print “Hello World”
class HelloWorld { public static void main(String args[]) { System.out.println("Hello World"); //Prints on screen “Hello World” } }
Output:
Hello World
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Program to Swap Two Numbers: The user gives two numbers as input and the numbers are swapped.
import java.util.Scanner; class SwapNumbers { public static void main(String args[]) { int z, y, temp; System.out.println("Enter z and y"); Scanner sct = new Scanner(System.in); //User inputs two numbers z = sct.nextInt(); //User inputs two numbers y = sct.nextInt(); System.out.println("Before Swapping\nz = "+z+"\ny = "+y); temp = z; //Swapping is done z = y; y = temp; System.out.println("After Swapping\nz = "+z+"\ny = "+y); } }
Output:
Enter z and y 5 10
Before Swapping
z = 5
y = 10
After Swapping
z = 10
y = 5
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Program to Display Date and Time
Current Date and time is printed on the screen
import java.util.*; class GetDateAndTime { public static void main(String args[]) { int day, month, year; int second, minute, hour; GregorianCalendar date = new GregorianCalendar(); //Creating Date Object day = date.get(Calendar.DAY_OF_MONTH);// Storing day of the Month month = date.get(Calendar.MONTH);// Storing the month year = date.get(Calendar.YEAR); // Storing the current Year second = date.get(Calendar.SECOND); //Time in Seconds, Minutes and Hours minute = date.get(Calendar.MINUTE); hour = date.get(Calendar.HOUR); System.out.println("Current date is "+day+"/"+(month+1)+"/"+year); System.out.println("Current time is "+hour+" : "+minute+" : "+second); } }
Output
Current date is 15/5/2014
Current time is 2 : 15 : 49
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Calculate the largest of three numbers: The largest of the three numbers entered by the user is calculated.
import java.util.Scanner; class Largest { public static void main(String args[]) { int a,b,c; System.out.println("Enter three integers "); Scanner sct = new Scanner(System.in); a = sct.nextInt(); b = sct.nextInt(); //User Input c = sct.nextInt(); if ( a > b && a > c ) // Condition check for Largest number System.out.println("1st number is largest."); else if ( b > a && b > c ) System.out.println("2nd number is largest."); else if ( c > a && c > b ) System.out.println("3rd number is largest."); else System.out.println("Number are not distinct."); } }
Output:
Enter three integers 6 10 7
2nd number is largest.
Factorial Calculation and a basic loop structure: The factorial of a number entered by the user is calculated.
import java.util.Scanner; class Factorial { public static void main(String args[]) { int n,c, fact = 1; System.out.println("Enter a number"); Scanner sct = new Scanner(System.in); n = sct.nextInt(); if ( n < 0 ) System.out.println("Number should be non-negative."); else { for ( c = 1 ; c <= n ; c++ ) // Calculating Factorial fact = fact*c; System.out.println("Factorial of "+n+" is = "+fact); } } }
Output
Enter a number 5
Factorial of 5 is = 120
Program to calculate Reverse of a number
import java.util.Scanner; class ReverseNumber { public static void main(String args[]) { int n, rev = 0; System.out.println("Enter the number to reverse "); Scanner sct = new Scanner(System.in); n = sct.nextInt(); //User Input while( n != 0 )// Reversing a Number Entered { rev = rev * 10; rev = rev + n%10; n = n/10; } System.out.println("Reverse of entered number is "+rev); } }
Output
Enter the number to reverse 5234
Reverse of entered number is 4325
Program to calculate Reverse of a String
import java.util.*; class ReverseString { public static void main(String args[]) { String original, reverse = ""; Scanner sct = new Scanner(System.in); System.out.println("Enter string to reverse"); original = sct.nextLine(); //String input from user int length = original.length(); for ( int i = length - 1 ; i>= 0 ; i-- ) // Reversing the String reverse = reverse + original.charAt(i); System.out.println("Reverse of entered string is: "+reverse); } }
Output
Enter a string to reverse I am a reverse
Reverse of entered string is: esrever a ma I
Retrieve a Substring in a String
import java.util.Scanner; class SubstringsOfAString { public static void main(String args[]) { String str, sub; int i, c, length; Scanner sct = new Scanner(System.in); System.out.println("Enter string to print all it's substrings:"); str = sct.nextLine(); // User input length = str.length(); System.out.println("Substrings of \""+str+"\" are :-"); for( c = 0 ; c < length ; c++ )// Calculating all the substring possible { for( i = 1 ; i<= length - c ; i++ ) { sub = str.substring(c, c+i); System.out.println(sub); } } } }
Output
Enter a string to print all substrings: funny
Substrings of “funny” are :-
f
fu
fun
funn
funny
u
un
unn
unny
n
nn
nny
n
ny
y
Searching using Linear Search Technique
import java.util.Scanner; class LinearSearch { public static void main(String args[]) { int c, n, search, array[]; Scanner sct = new Scanner(System.in); System.out.println("Enter number of elements"); n = sct.nextInt(); array = new int[n]; System.out.println("Enter " + n + " integers"); for (c = 0; c < n; c++) //User input of array values { array[c] = sct.nextInt(); } System.out.println("Enter value to find"); //User input of number to Search search = sct.nextInt(); for (c = 0; c < n; c++) { if (array[c] == search) // element is present { System.out.println(search + " present at location " + (c + 1) + "."); break; } } if (c == n) /* element is absent */ System.out.println(search + " not present inside array."); } }
Output
Enter number of elements 5
Enter 5 integers 8 9 7 5 0
Enter value to find 5
5 present at location 4.
Search using Binary Search Technique
The binary search is quick and is used in sorted array. The binary search starts the element search from middle of the array and proceeds further up or down the array depending on the mid value of the array.
import java.util.Scanner; class BinarySearch { public static void main(String args[]) { int c, first, last, middle, n, search, array[]; Scanner sct = new Scanner(System.in); System.out.println("Enter number of elements"); n = sct.nextInt(); array = new int[n]; System.out.println("Enter " + n + " integers"); for (c = 0; c < n; c++) { array[c] = sct.nextInt(); } System.out.println("Enter value to find"); search = sct.nextInt(); first = 0; // Basic binary search last = n - 1; middle = (first + last)/2; while( first <= last ) { if ( array[middle] < search ) first = middle + 1; else if ( array[middle] == search ) { System.out.println(search + " found at location " + (middle + 1) + "."); break; } else { last = middle - 1; } middle = (first + last)/2; if ( first > last ){ System.out.println(search + " is not present in the list.\n"); } } }
Output
Enter number of elements 5
Enter 5 integers 3 5 7 8 9
Enter value to find 8
8 present at location 4.
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