Hollow Diamond Pattern in Java

There are many pattern programs are written in Java by programmers for coding practice and cracking interviews. The pattern programs are usually asked in interviews to check the logical thinking and its implementation in program. In this section, we will create Java programs to print hollow diamond patterns using a while loop, do-while loop, and for loop.

In the hollow diamond pattern, the first and last row contains only a star, and the rest of the rows contains two stars. We can replace star (*) with any other symbol that we want to print.

To print the hollow diamond pattern (as shown in the following figure), we will break the pattern into two sections i.e. upper and lower. Also, we will implement the logic for the upper and lower sections, separately. The logic is applied to all patterns discussed in this section.

Let's implement the logic in the Java program.

Using for Loop

HollowDiamondPattern1.java

import java.util.Scanner;
public class HollowDiamondPattern1
{
public static void main(String args[])
{
Scanner scan=new Scanner(System.in);
System.out.print("Enter the number of rows: ");
//reads an integer (rows) from the user
int rows=scan.nextInt();
System.out.print("Enter the symbol you want to print: "); 
//reads the symbol from the user
char symbol=scan.next().charAt(0);
//prints upper section of the pattern
for(int i=1; i<=rows; i++)
{
for(int j=rows; j>i; j--)
{
//prints space      
System.out.print(" ");
}
//prints symbol
System.out.print(symbol);
for(int j=1; j<(i-1)*2; j++)
{
//prints space    
System.out.print(" ");
}
if(i==1)
{
//throws cursor to the next line    
System.out.print("\n");
}
else
{
//prints symbol and throws cursor to the next line        
System.out.print(symbol+"\n");
}
}  
//prints lower section of the pattern
for(int i=rows-1; i>=1; i--)
{
for(int j=rows; j>i; j--)
{
//prints space        
System.out.print(" ");
}
//prints symbol
System.out.print(symbol);
for(int j=1; j<(i-1)*2; j++)
{
//prints space    
System.out.print(" ");
}
if(i==1)
{
//throws cursor to the next line        
System.out.print("\n");
}
else
{
//prints symbol and throws cursor to the next line     
System.out.print(symbol+"\n");
}
}
}
}

Output:

In the above program, we observe that to print the lower half pattern, we have done only changes in the first for loop, the rest of the code is the same.

change to:

Using while Loop

In the following Java program, we have replaced the for loop with the while loop only.

HollowDiamondPattern2.java

import java.util.Scanner;
public class HollowDiamondPattern2
{
public static void main(String args[])
{
int i,j;
Scanner scan=new Scanner(System.in);
System.out.print("Enter the number of rows: ");
//reads an integer (rows) from the user
int rows=scan.nextInt();
System.out.print("Enter the symbol you want to print: "); 
//reads the symbol from the user
char symbol=scan.next().charAt(0);
i=1;
//prints upper section of the pattern
while(i<=rows)
{
j=rows;
while(j>i)
{
System.out.print(" ");
j--;
} //end of while
System.out.print(symbol);
j=1;
while(j<(i-1)*2)
{
System.out.print(" ");
j++;
}  //end of while
if(i==1)
{
//throws cursor to the next line        
System.out.print("\n");
}
else
{
//prints symbol and throws cursor to the next line         
System.out.print(symbol+"\n");
}
i++;
} //end of while loop
//prints lower section of the pattern
i=rows-1;
while( i>=1)
{
j=rows;
while(j>i)
{
System.out.print(" ");
j--;
}
//prints symbol
System.out.print(symbol);
j=1;
while(j<(i-1)*2)
{
System.out.print(" ");
j++;
} //end of while loop
if(i==1)
{
//throws cursor to the next line        
System.out.print("\n");
}
else
{
//prints symbol and throws cursor to the next line            
System.out.print(symbol+"\n");
}
i--;
} //end of while loop
}
}
Out

Output:

Using do-while Loop

HollowDiamondPattern3.java

import java.util.Scanner;
public class HollowDiamondPattern3
{
public static void main(String args[])
{
int i,j;
Scanner scan=new Scanner(System.in);
System.out.print("Enter the number of rows: ");
//reads an integer (rows) from the user
int rows=scan.nextInt();
System.out.print("Enter the symbol you want to print: "); 
//reads the symbol from the user
char symbol=scan.next().charAt(0);
i=1;
//prints upper section of the pattern 
//executes until the condition i<=rows become false
do
{
j=rows;
//executes until the condition j>=i becomes false
do
{
//prints space    
System.out.print(" ");
j--;
} //end of do
while(j>=i);
System.out.print(symbol);
j=1;
//executes until the condition (j<(i-1)*2) becomes false
do
{
//prints space    
System.out.print(" ");
j++;
} //end of do
while(j<(i-1)*2);
if(i==1)
{
//throws cursor to the next line            
System.out.print("\n");
}
else
{
//prints symbol and throws cursor to the next line             
System.out.print(symbol+"\n");
}
i++;
} //end of do
while(i<=rows);
i=rows-1;
//prints lower section of the pattern
//executes until the condition i>=1 becomes false
do
{
j=rows;
//executes until the condition j>=i becomes false
do
{
//prints space    
System.out.print(" ");
j--;
}
while(j>=i);
//prints symbol
System.out.print(symbol);
j=1;
//executes until the condition (j<(i-1)*2) becomes false
do
{
//prints space    
System.out.print(" ");
j++;
}  //end of do
while(j<(i-1)*2);
if(i==1)
{
//throws cursor to the next line            
System.out.print("\n");
}
else
{
//prints symbol and throws cursor to the next line             
System.out.print(symbol+"\n");
}
i--;
}  //end of do
while(i>=1);
}
}

Output:

Let's see another hollow diamond pattern.

To print the following hollow diamond pattern, we will divide the pattern into two sections i.e. upper and lower (as shown in the following figure). Also, we will implement the logic for the upper and lower sections, separately. The upper section contains the first five rows and the lower section contains the last five rows of the diamond pattern.

First, will create a 10*10 matrix. Print the first row with the symbol (*). In the next row (2^nd), there are two spaces. We have to calculate space. In the upper section, we observe that the space is going doubled and in the lower section space is decreasing by 2.

So, we can calculate the space by using the generalized formula 2*i-2 (where i is the row number). Suppose, we have to calculate space for the third row. 2*3-2 = 4 (space). In the following program, we have used the variable i for rows, j for columns, and k for spaces.

HollowDiamondPattern4.java

public class HollowDiamondPattern4
{
public static void main(String args[])
{ 
//logic to print the first half pattern 
for(int i=1; i<=10; i++)
{
for(int j=1; j<=10-i+1; j++)
{
System.out.print("*");
} 
//loop calculates space
for(int k=1; k<=2*i-2; k++)
{
System.out.print(" ");
} 
for(int j=1; j<=10-i+1; j++)
{
System.out.print("*");
} 
System.out.println();
}
//logic to print the second half pattern 
for(int i=9; i>=1; i--)
{
for(int j=i; j<=10; j++)
{
System.out.print("*");
} 
//loop calculates space
for(int k=1; k<=(2*i)-2; k++)
{
System.out.print(" ");
} 
for(int j=i; j<=10; j++)
{
System.out.print("*");
} 
System.out.println();
}
} 
}

Output: