在 Java 中打印简单模式

Question

Could someone explain the basics behind printing simple patterns in Java?

I'll give one specific example.

I'd just like for someone to clarify what each line is doing so I get a better understanding of how this works. Any other explained examples (line by line) would also be appreciated!

public static void drawPyramidPattern() {
    for (int i = 0; i < 5; i++) {
        for (int j = 0; j < 5 - i; j++) {
            System.out.print(" ");
        }
        for (int k = 0; k <= i; k++) {
            System.out.print("* ");
        }
        System.out.println();
    }
}

Answer 1

Printing anything or everything via a loop is just about understanding the flow of execution. In your code also, if you'll start watching the flow line by line you'll come to know that how it is working exactly.

If you understand how it works, you would be able to print any pattern, but basics should be clear. Try printing variable i, j and k values after each iteration. See the values that how that gets changed after each cycle of execution and then see the logic you've applied.

Your question is somewhat very broad in scope and can not be answered exactly unless narrowed it down. I would suggest to run this line by line and watch the output, try more changes even if it doesn't make any sense, you'll be having a good understanding over looping even for all of your future tasks. And if after trying yourself, you come to any problem, share here, people are ready to solve them. :)

Hope this helps.

Answer 2

First you must a have complete understanding of loops, nested loops then you come up to patterns designing.

1) First run the loops in hard form like on Register/on Page for understanding the loops.
2) Use debugger to identify the loop progress.

Answer 3

If you think about it in terms of mathematics, loops are just functions.

A single for loop would just be x.

Example

for (int i = 0; i < 5; i++) {
System.out.println("This is function x.");
}

However when you start nesting loops it because a greater function. A for loop inside another for loop would be a function x^2

For example:

for (int i = 0; i < 5; i++) {
     for (int j = 0; J < 5; j++){
     System.out.println("This is the j loop");
     }
     System.out.println("This is the i loop");
}

The reason behind this is because in order to finish the first iteration of i, everything inside the loop must be completed. But, the i loop has another loop inside of it, so that must be finished first. So the loop with j must execute until it is finished. (In this case 5 times), Great, now we can increment i. But now we have to step through j again! This process continues until i reaches its threshold of being < 5. So the output would look something like this

Output:
This is the j loop
This is the j loop
This is the j loop
This is the j loop
This is the j loop
This is the i loop
This is the j loop
This is the j loop
....

This would continue until the i has reached 5, in which case it no longer satisfies the necessary i < 5, and the loop would end. Hopefully this helps

Answer 4

First, since i = 0 & 0<5 is true you enter the first(outer) for-loop.

Remember i = 0.

Then j = 0; but 0 < i = 0 is false so you don't enter the second loop.

For the third loop, k = 0 & 0<=0 is true. So you enter the loop and execute the print statement, ie print a star.

k++, this will increment k by 1 and check the boolean; You ask yourself is 1 <= 0; clearly no ; so you exit the for-loop and then reach the println statement which will take you to the next line.

And then you go back to the outer loop.

Answer 5

//this code print Diagonal Pattern if matrix is 1 2 3 4 5 6 7 8 9 output is : 1 4 2 7 5 3 8 6 9

import java.util.*;
class DiagonalPattern
{
    public static void main(String args[])
    {
        Scanner sc=new Scanner(System.in);
        int x[][];
        int i,j,row,col,p,temp=1,last=0;
        System.out.println("how many array wants to create and size of array");
        row=sc.nextInt();
        col=sc.nextInt();
        x=new int[row][col];
        System.out.println("Enter  " +row*col+ "  elements of array of array");
            for(i=0;i<row;i++)
            {
            for(j=0;j<col;j++)
            {
                x[i][j]=sc.nextInt();
                last=j;
            }
            }
        for(i=0;i<row;i++)
            {
            System.out.println("");
            int k=i;
            for(j=0;j<=i;j++,k--)
            {
                if(j==col)
                {
                    break;
                }
                else
                {
                    System.out.print(x[k][j]);  
                System.out.print(" ");
                }
            }
            }
        for(p=x.length;p>0;p--,temp++)
            {
            System.out.println("");
            i=x.length-1;
            int k=i;
            for(j=temp;j<=last;j++,k--)
            {
                System.out.print(x[k][j]);  
                System.out.print(" ");
            }
            }   
    }
}