使用Java for循环绘制形状

Question

I'm just getting started with Java and my teacher asked me to draw the following two shapes using nested for loops.

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

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

However, I was able to draw the first figure using the following code.

class TriangleDrawing{

    public static void main(String args[]){

        for(int x = 1; x <= 6; x++){

            for(int y = 1; y <= (6-x); y++){

                System.out.print(" ");

            }

            for(int z = 0; z < (x + (x-1)); z++){

                System.out.print("*");

            }

            for(int p = 1; p <= (6-x); p++){

                System.out.print(" ");

            }

            System.out.println();

        }

    }

}

I'm having trouble with drawing the second figure.
Can anyone help me out drawing that one, by using nested for loops?

Answer 1

It appears to me that the second figure is simply the first figure with the internal asterisks replaced with spaces.

That means you only have to change the z -loop so that, on each line but the first and last, it:

• prints one asterisk;
• prints N spaces, where N starts at one for the second line, and increases by two for each line you're on; and
• print the final asterisk.

For the first and last lines, the code will need to stay the same. For the former, you only want one asterisk, for the latter, you want all asterisks.

And, as an aside, the third loop is totally unnecessary. There's no point putting spaces at the end of the line (in this case) since no-one can see them.

---

Since it's classwork, I urge you to try and implement that yourself. For completeness, I include the solution below:

public class Test {
    public static void main(String args[]){
        int sz = 6;

        // First line "*"

        for (int y = 1; y < sz; y++)
            System.out.print(" ");
        System.out.println("*");

        // Middle lines "*   *"

        for (int x = 2; x < sz; x++) {
            for (int y = 1; y <= sz - x; y++)
                System.out.print(" ");
            System.out.print("*");
            for (int y = 1; y < x * 2 - 2; y++)
                System.out.print(" ");
            System.out.println("*");
        }

        // Final line "*****"

        System.out.print("*");
        for (int y = 1; y < sz * 2 - 2; y++)
            System.out.print("*");
        System.out.println("*");
    }
}

Answer 2

In this block:

for(int z = 0; z < (x + (x-1)); z++){

  System.out.print("*"); } 

check whether you are in the first and/or last element. if so, print '*' else, print " "

Answer 3

change your for loop which is printing * as:

 for(int z = 0; z < (x + (x-1)); z++){
        if(z==0 || z ==(x + (x-1))-1 || x==6)
                System.out.print("*");
        else
                System.out.print(" ");

    }

instead of

for(int z = 0; z < (x + (x-1)); z++){

            System.out.print("*");

        }