Java Program to Print Diamond Shape Star Pattern

In this article, we are going to learn how to print diamond shape star patterns in Java. 

Illustration:

Input: number = 7
 
Output:

       *
      ***
     *****
    *******
   *********
  ***********
 *************
  ***********
   *********
    *******
     *****
      ***
       *

Methods: When it comes to pattern printing we do opt for standard ways of printing them via loops only. We will try out different types of loops to print the same pattern.

Example 1: Using do-while Loop

Java

// Java program to Print Diamond Star Pattern
// Using do-while loop

// Importing input output classes
import java.io.*;

// Main class
public class GFG {

    // Main driver method
    public static void main(String[] args)
    {
        // Declaring and initializing variables

        // Variable initialized to the row where max star
        // should be there as after that they decreases to
        // give diamond pattern
        int number = 7;

        // Diamond starting with single star in first row,so
        // initialized
        int m = 1;

        // Columnar printing
        int n;

        // Outer loop 1
        // Prints the first half diamond
        do {
            n = 1;

            // Inner loop 1
            // Prints space until ++n <= number - m + 1 is
            // false
            do {
                // Print whitespace between
                System.out.print(" ");

            }

            // Condition for inside do-while loop 1
            while (++n <= number - m + 1);

            // Now
            n = 1;

            // Inner loop 2
            // Prints star until ++n <= m * 2 - 1 is false

            do {

                // Print star
                System.out.print("*");
            }

            // Condition for inner do-while loop 2
            while (++n <= m * 2 - 1);

            // A new row requires a new line
            System.out.println();

        }

        // Condition for outer do-while loop 1
        while (++m <= number);

        // Now we are done with printing the upper half
        // diamond.

        // Note: Not to print the bottom row again in lower
        // half diamond printing Hence variable to be
        // initialized should one lesser than number
        m = number - 1;

        // Outer loop 2
        // Prints the second half diamond
        do {
            n = 1;

            // Inner loop 1
            // Prints space until ++n <= number - m + 1 is
            // false
            do {
                // Print whitespace between
                System.out.print(" ");

            } while (++n <= number - m + 1);

            n = 1;

            // Inner loop 2
            // Prints star until ++n <= m * 2 - 1 is false
            do {
                // Prints star
                System.out.print("*");

            } while (++n <= m * 2 - 1);

            // By now done with one row of lower diamond
            // printing so a new line is required
            System.out.println();

        }

        // Condition for outer do-while loop 2
        while (--m > 0);
    }
}

Output

       *
      ***
     *****
    *******
   *********
  ***********
 *************
  ***********
   *********
    *******
     *****
      ***
       *

Time complexity: O(n^2) where n is given input number
Auxiliary Space: O(1) 

Example 2: Using while Loop

Java

// Java program to print diamond star pattern
// Using while loop

// Importing input output classes
import java.io.*;

// Main class
public class GFG {

    // Main driver method
    public static void main(String[] args)
    {

        // Declaring and initializing variables

        // Variable initialized to the row where max star
        // should be there as after that they decreases to
        // give diamond pattern
        int number = 7;

        // Diamond starting with single star in first row
        int m = 1;

        // Columnar printing
        int n;

        // Outer loop 1
        // Prints the first half diamond

        // Condition holding true till
        // number of rows initialized
        while (m <= number) {
            n = 1;

            // Inner loop 1
            // Prints space until n++ <= number - m is false
            while (n++ <= number - m) {

                // Print whitespaces inbetween
                System.out.print(" ");
            }

            n = 1;

            // Inner loop 2
            // Prints star until n++ <= m * 2 - 1 is false
            while (n++ <= m * 2 - 1) {

                // Print star
                System.out.print("*");
            }

            // By now we are done for above pyramid printing
            // ending line after each row
            System.out.println();

            // Incrementing as we want pyramid generation
            m++;
        }

        // Now we are done with printing the upper half
        // diamond.

        // Note: Not to print the bottom row again in lower
        // half diamond printing Hence variable t be
        // initialized should one lesser than number
        m = number - 1;

        // Outer loop 2
        // Prints the second half diamond
        while (m > 0) {
            n = 1;

            // Inner loop 1
            // Prints spaces until n++ <= number - m is
            // false
            while (n++ <= number - m) {

                // Print whitespace in between
                System.out.print(" ");
            }

            n = 1;

            // Inner loop 2
            // Prints star until n++ <= m * 2 - 1 is false
            while (n++ <= m * 2 - 1) {

                // Print star
                System.out.print("*");
            }

            // Ending line after each row
            System.out.println();

            // Decrementing as we want reverse pyramid
            // generation
            m--;
        }
    }
}

Output

       *
      ***
     *****
    *******
   *********
  ***********
 *************
  ***********
   *********
    *******
     *****
      ***
       *

Example 3: Using for Loop

Java

// Java program to print diamond star pattern
// Using for loop

// Importing  input output classes
import java.io.*;

// Main class
public class GFG {

    // Main driver method
    public static void main(String[] args)
    {

        // Declaring and initializing variables

        // Variable initialized to the row where max star
        // should be there as after that they decreases to
        // give diamond pattern
        int number = 7;

        int m, n;

        // Outer loop 1
        // prints the first half diamond
        for (m = 1; m <= number; m++) {

            // Inner loop 1 print whitespaces inbetween
            for (n = 1; n <= number - m; n++) {
                System.out.print(" ");
            }

            // Inner loop 2 prints star
            for (n = 1; n <= m * 2 - 1; n++) {
                System.out.print("*");
            }

            // Ending line after each row
            System.out.println();
        }

        // Outer loop 2
        // Prints the second half diamond
        for (m = number - 1; m > 0; m--) {

            // Inner loop 1 print whitespaces inbetween
            for (n = 1; n <= number - m; n++) {
                System.out.print(" ");
            }

            // Inner loop 2 print star
            for (n = 1; n <= m * 2 - 1; n++) {
                System.out.print("*");
            }

            // Ending line after each row
            System.out.println();
        }
    }
}

Output

      *
     ***
    *****
   *******
  *********
 ***********
*************
 ***********
  *********
   *******
    *****
     ***
      *

Time Complexity : O(n²)
Auxiliary Space : O(1)