Pattern Programs in Java
Pattern Programs in Java
In Java, pattern programs are the most important from the perspective of interviews. The pattern programs improve thinking and coding skills. It also helps us to develop a firm grip on looping concepts. In this section, we will create different pattern programs.
We have categorized the pattern programs into the following different categories.
- Character/ Alphabet Patterns
- Numeric/ Number Patterns
- Star Patterns
Character/ Alphabet Patterns
1. Right Triangle Pattern
Filename: RightTrianglePatternExample.java
public class RightTrianglePatternExample{
public static void main(String[] args)
{
int firstAlphabet = 65; // ASCII value of the character ‘A’
int row = 8; //defines number of rows
//The loop takes care of the row.
for(int r = 0; r < row; r++)
{
// The loop handles column
for(int c = 0; c <= r; c++)
{
System.out.print((char)(firstAlphabet) + " ");
}
System.out.println(); // moves the cursor to the next line
}
}
}
Output:
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Explanation: Let us understand the working of code. The first two lines written in the main method are straight-forward. We are assigning values to the variables firstAlphabet and row. Now, consider the following code snippet taken from above.
for(int r = 0; r < row; r++)
{
for(int c = 0; c <= r; c++)
{
System.out.print((char)(firstAlphabet) + " ");
}
System.out.println();
}
In the above-written code snippet, we have two nested for loops. The outer loop deals with the rows and columns are taken care of by the inner loop. The outer loop runs eight times from 0 to 8.
Iteration 1:
For r =0, 0 < 8 (true) For c =0, 0 <= 0 (true)
Output:
A
The inner loop runs only once, as it starts from zero and ends at 1, and the print-statement of the inner for loop prints the character A. The control now shifts to the println-statement, which prints nothing but forces the cursor to embark on its journey from the next line. The variable r gets incremented by one and gets the value 1.
Iteration 2:
For r =1, 1 < 8 (true) For c =0, 0 <= 1 (true)
Output:
A A A
In the second iteration, the inner loop runs two times (from 0 to 1 and from 1 to 2), and print-statement also prints the character A twice. The cursor again jumps to the next line. Finally, the variable r gets incremented by one and gets the value 2.
Iteration 3:
For r =2, 2 < 8 (true) For c =0, 0 <= 2 (true)
Output:
A A A A A A
At this time the inner loop runs three times (0 to 3) and prints the character A thrice. The cursor again moves to the next line, and the variable r gets the value 3.
Iteration 4:
For r =3, 3 < 8 (true) For c =0, 0 <= 3 (true)
Output:
A A A A A A A A A A
Now, the inner loop executes four times (0 to 4). Hence, we get the character A four times in the fourth row. Again, the cursor shifts to the next line, and the variable r is now 4.
Iteration 5
For r =4, 4 < 8 (true) For c =0, 0 <= 4 (true)
Output:
A A A A A A A A A A A A A A A
At this time, we get the character A five times (0 to 5), and the r variable gets the value 5. The cursor is again placed at the next line.
Iteration 6:
For r =5, 5 < 8 (true) For c =0, 0 <= 5 (true)
Output:
A A A A A A A A A A A A A A A A A A A A A
Now the iteration of the inner loop is from 0 to 6, i.e., six times. Therefore, we see six times A. The cursor is again ready to print from the next line. The value of the r variable is 6.
Iteration 7:
For r =6, 6 < 8 (true) For c =0, 0 <= 6 (true)
Output:
A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Now, we can easily guess why we are getting seven times A. The r variable is now 7.
Iteration 8:
For r =7, 7 < 8 (true) For c =0, 0 <= 7 (true)
Output:
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
At this time, we get the character A eight times. The r variable gets incremented to 8. In the next iteration, the condition for the r variable evaluates false (8 < 8), and the outer loop terminates, and eventually, the program execution ends.
2. Repeating Right Triangle Pattern
Filename: RepeatingRightTrianglePatternExample.java
public class RepeatingRightTrianglePatternExample
{
public static void main(String[] argvs)
{
int firstAlphabet = 65; // 65 is the ASCII value the ‘A’ character
int row = 8; //defines number of rows
//the loop takes care of the row
for(int r = 0; r < row; r++)
{
// the loop handles column
for(int c = 0; c <= r; c++)
{
System.out.print((char)(firstAlphabet + c) + " ");
}
System.out.println(); // moves the cursor to the next line
}
}
}
Output:
A A B A B C A B C D A B C D E A B C D E F A B C D E F G A B C D E F G H
3. Another Repeating Right Triangle Pattern
Filename: RepeatingRightTrianglePatternExample1.java
public class RepeatingRightTrianglePatternExample1
{
public static void main(String[] argvs)
{
int firstAlphabet = 65; // 65 is the ASCII value the ‘A’ character
int row = 8; //defines number of rows
//The loop takes care of the row.
for(int r = 0; r < row; r++)
{
// The loop handles column
for(int c = 0; c <= r; c++)
{
System.out.print((char)(firstAlphabet) + " ");
}
firstAlphabet++;
System.out.println(); // moves the cursor to the next line
}
}
}
Output:
A B B C C C D D D D E E E E E F F F F F F G G G G G G G
4. Character-Triangle Pattern
Filename: CharacterTrianglePatternExample.java
public class CharacterTrianglePatternExample
{
public static void main(String[] argvs)
{
int firstAlphabet = 65; // 65 is the ASCII value the ‘A’ character
int row = 8; //defines number of rows
//The loop takes care of the row.
for(int r = 0; r < row; r++)
{
//The loop deals with the indentation process
for(int indent = row; indent >= r; indent--)
System.out.print(" ");
// The loop handles column
for(int c = 0; c <= r; c++)
{
System.out.print((char)(firstAlphabet + c) + " ");
}
System.out.println(); // moves the cursor to the next line
}
}
}
Output:
A A B A B C A B C D A B C D E A B C D E F A B C D E F G
5. Character-Diamond Pattern
Filename: CharacterTrianglePatternExample.java
public class CharacterTrianglePatternExample
{
public static void main(String[] argvs)
{
int firstAlphabet = 65; // 65 is the ASCII value the ‘A’ character
int row = 8; //defines number of rows
//The loop takes care of the row.
for(int r = 0; r < row; r++)
{
//The loop deals with the indentation
for(int indent = row; indent >= r; indent--)
System.out.print(" ");
//character 'A' is printed only once
if(firstAlphabet != 65)
System.out.print((char)(firstAlphabet));
// The loop handles white spaces between characters
// in a single row
for(int c = -1; c <= 2*r-1; c++)
{
System.out.print(" ");
}
System.out.print((char)(firstAlphabet));
//Moving to the next character
++firstAlphabet;
System.out.println(); // moves the cursor to the next line
}
//The following section of code prints
//the second half of the diamond
//We will be printing character starting from the
//second last row.
firstAlphabet-=2;
for(int r = row - 2; r >= 0; r--)
{
//The loop deals with the indentation process
for(int indent = row; indent >= r; indent--)
System.out.print(" ");
//Again, ‘A’ is printed only once
if(firstAlphabet != 65)
System.out.print((char)(firstAlphabet));
// The loop handles inter-space between characters
for(int c = -1; c <= 2*r-1; c++)
{
System.out.print(" ");
}
System.out.print((char)(firstAlphabet));
//Move to the previous character
--firstAlphabet;
System.out.println(); // moves the cursor to the next line
}
}
}
Output:
A B B C C D D E E F F G G H H G G F F E E D D C C B B A
6. Character Pattern – K Shaped
Filename: KShapedPatternExample.java
public class KShapedPatternExample
{
public static void main(String[] argvs)
{
int firstAlphabet = 65; // 65 is the ASCII value the ‘A’ character
int row = 8; //defines number of rows
//The loop takes care of the row.
for(int r = 0; r < row; r++)
{
// The loop handles column
for(int c = 0; c < row - r; c++)
{
System.out.print((char)(firstAlphabet + c) + " ");
}
System.out.println(); // moves the cursor to the next line
}
// The section of code prints the second half of the K – shaped pattern
for(int r = 1; r < row; r++)
{
for(int c = 0; c <= r; c++)
{
System.out.print((char)(firstAlphabet + c) + " ");
}
System.out.println(); // moves the cursor to the next line
}
}
}
Output:
A B C D E F G H A B C D E F G A B C D E F A B C D E A B C D A B C A B A A B A B C A B C D A B C D E A B C D E F A B C D E F G A B C D E F G H
Numeric/ Number Patterns
Filename: NumericPatternExample.java
public class NumericPatternExample
{
public static void main(String[] argvs)
{
int row = 5;
int r, c, j;
for(r = 0; r < row; r++) //The loop handles rows
{
for(j = 2*(row - r); j >= 0; j--) //Different indentation for different rows
{
System.out.print(" "); // printing space
}
for(c = 0; c <= r; c++) // The loop handles columns
{
System.out.print(c + 1 + " "); // Displaying numbers
}
System.out.println(); // Forcing line break after each row
}
}
}
Output:
1 1 2 1 2 3 1 2 3 4 1 2 3 4 5
Star Patterns
Filename: StarPatternExample.java
public class StarPatternExample
{
public static void main(String[] argvs)
{
int row = 5;
int r, c, j;
for(r = 0; r < row; r++) //The loop handles rows
{
for(j = 2*(row - r); j >= 0; j--) //Different indentation for different rows
{
System.out.print(" "); // printing space
}
for(c = 0; c <= r; c++) // The loop handles columns
{
System.out.print("* "); // Displaying stars
}
System.out.println(); // Forcing line break after each row
}
}
}
Output:
* * * * * * * * * * * * * * *
We will discuss other pattern programs in the coming sections.