Java编译中无关的内容

Question

Can someone be so kind to let me know why the heck javac is printing extra lines with zeros when executed the following lines of code? I have intentionally printed the number of possible lines in the first line, which is exactly equal to the number of nonzero lines. Any advice? Code:

int[] fa = new int[15];
    int[][] sa = new int[100][3];
    int a=0, b=0;

    for(int i=0; i<15; i++){
        fa[i] = i+1;
    }


    for(int i=0; i<fa.length; i++){
        for(int j=i+1; j<fa.length; j++){
            for(int k=j+1; k<fa.length; k++){
                if(fa[i]+fa[j]+fa[k]==15){
                    sa[a][0] = fa[i];
                    sa[a][1] = fa[j];
                    sa[a][2] = fa[k];
                    a++;
                }
            }
        }
    }
    System.out.println(a);
    for(int i=0; i<sa.length; i++){
        for(int j=0; j<3; j++){
            System.out.print(sa[i][j]+" ");
        }
        System.out.println();
    }

The output:

 12 1 2 12 1 3 11 1 4 10 1 5 9 1 6 8 2 3 10 2 4 9 2 5 8 2 6 7 3 4 8 3 5 7 4 5 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Answer 1

To print you are iterating on sa :

for(int i=0; i<sa.length; i++){

And at the beginning you stated it has 100 rows ( default values to 0 ):

int[][] sa = new int[100][3];

It shows those 100 rows independently of what you did on your second for with fa .

Try with:

for(int i=0; i<a; i++){
    for(int j=0; j<3; j++){
        System.out.print(sa[i][j]+" ");
    }
    System.out.println();
}

Answer 2

You are printing the content of the entire sa regardless of how many items you have added to it. The first 12 items print correctly, while the remaining items print the initial values of int[3] arrays, which happen to be zeros.

You can fix this by iterating up to a items, like this:

for(int i=0; i < a; i++) {
//              ^^^ 
    for(int j=0; j<3; j++){
        System.out.print(sa[i][j]+" ");
    }
    System.out.println();
}

Alternatively, you could switch to using lists in place of arrays. Since lists grow dynamically, you would be able to avoid this problem altogether:

class Triple {
    private final a, b, c;
    public Triple(int a, int b, int c) {this.a=a; this.b=b; this.c=c;}
    public int getA() { return a; }
    public int getB() { return b; }
    public int getC() { return c; }
}

List<Triple> sa = new ArrayList<>();
...
if(fa[i]+fa[j]+fa[k]==15){
    sa.add(new Triple(fa[i], fa[j], fa[k]));
}
...
for (Triple t : sa) {
    ...
}