这段代码能更有效吗？

Question

This Program should do this

N 10*N 100*N 1000*N
1 10  100    1000
2 20  200    2000
3 30  300    3000
4 40 400     4000
5 50 500    5000

So here's my code:

public class ex_4_21 {

    public static void main( String Args[] ){

    int process = 1;
    int process2 = 1;
    int process22 = 1;
    int process3 = 1;
    int process33 = 2;

    System.out.println("N   10*N   100*N   1000*N");
    while(process<=5){

        while(process2<=3){
        System.out.printf("%d   ",process2);

        while(process22<=3){
            process2 = process2 * 10;
            System.out.printf("%d     ",process2);
            process22++;
        }
        process2++;
        }


        process++;
    }

    }
}   

Can my code be more effecient? I am currently learning while loops. So far this what I got. Can anyone make this more efficient, or give me ideas on how to make my code more efficient?

This is not a homework, i am self studying java

Answer 1

You can use a single variable n to do this.

 while(n is less than the maximum value that you wish n to be)
     print n and a tab
     print n * 10 and a tab
     print n * 100 and a tab
     print n * 1000 and a new line
     n++

if the power of 10 is variable then you can try this:

 while(n is less than the maximum value that you wish n to be)
    while(i is less than the max power of ten)
        print n * i * 10 and a tab
        i++
    print a newline
    n++

Answer 2

If you must use a while loop

public class ex_4_21 {

public static void main( String Args[] ){

int process = 1;

System.out.println("N   10*N   100*N   1000*N");
while(process<=5){

    System.out.println(process + "  " + 10*process + "  " + 100*process + "  " + 1000*process + "\n");
    process++;
}

}
}

Answer 3

You have one too many while loops (your "process2" while loop is unnecessary). You also appear to have some bugs related to the fact that the variables you are looping on in the inner loops are not re-initialized with each iteration.

I would also recommend against while loops for this; Your example fits a for loop much better; I understand you are trying to learn the looping mechanism, but part of learning should also be in deciding when to use which construct. This really isn't a performance recommendation, more an approach recommendation.

I don't have any further performance improvement suggestions, for what you are trying to do; You could obviously remove loops (dropping down to a single or even no loops), but two loops makes sense for what you are doing (allows you to easily add another row or column to the output with minimal changes).

Answer 4

You can try loop unrolling, similar to @Vincent Ramdhanie's answer.

However, loop unrolling and threading won't produce a significant performance improvement for such a small sample. The overhead involved in creating and launching threads (processes) takes more time than a simple while loop. The overhead in I/O will take more time than the unrolled version saves. A complex program is harder to debug and maintain than a simple one.

You're thinking is called microoptimization . Save the optimizations for larger programs and only when the requirements cannot be met or the customer(s) demand so.