Thread: inverting rows and lines of a matrix

i don't think it's quite correct:

Please explain. Post the program's current output and add comments saying what is wrong with it.

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Actually it doesn't work, It gives me: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1

The idea is to switch each element with his opposite, so I've thought to do 4 cycles E(i,j) <-> E(k,s)

K=2

E(0,0) <-> E(k,k)
E(0,1)<->E(k,k-1)
E(0,2)<->E(k,k-2)

E(1,0)->E(k-1,k)
E(1,1)->E(k-1,k-1)
E(1,2)->E(k-1,k-2)

E(2,0)->E(k-2,k)
E(2,1)->E(k-2,k-1)
E(2,2)->E(k-2,k-2)

        for(int i=0;i<mat_simmetrica.length;i++){
                for(int k=mat_simmetrica.length;k>0;k--) {
                    for(int j=0;j<mat_simmetrica.length;j++){
                    for (int s = mat_simmetrica.length; s > 0; s--) {
 
                        Bin<Double,Integer> element = new Bin<>();
 
                        element= mat_simmetrica[i][j];
                        mat_simmetrica[i][j]=mat_simmetrica[k][s];
                        mat_simmetrica[k][s]=element;
 
                    }
                    j++;
                }
 
            }
           i++;
        }

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
What variable has the -1?

Where does the code use a negative index? Zero minus 1 = -1
The code should not subtract from a 0 index