Strange characters when executing a method to add arrays

Good morning guys, I'm a beginner in Java and I have a problem here. Can someone tell me what these strange characters appear in the console when executing a matrix sum method (I'm using Threads)?

Matrixsummethod:

publicclasssomaMatriz{publicint[][]matriz(int[][]m1,int[][]m2){intsize=m1.length;int[][]c=newint[size][size];RunnablethreadMatriz1=newRunnable(){publicvoidrun(){try{for(inti=0;i<size;++i){for(intj=0;j<size;++j){//\ttemfunçãodetabulação//\ntemfunçãodequebralinhac[i][j]=m1[i][j]+m2[i][j];System.out.printf("%d\t",c[i][j]);  
                            } 
                              System.out.printf("\n");
                        }   

                        Thread.sleep(1000); //Para demorar um segundo
                    } catch (InterruptedException e) {
                        System.out.println("A Thread sofreu uma interrupcao!");
                    }

            }
        };

        Thread th1 = new Thread(threadMatriz1);
        th1.start();

        return c; 

    }

}

Main to call the Matrix method:

package trabSD23;

public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        int [][] ar1 = { {1,2,3}, {4,5,6}, {6,8,2} };
        int [][] ar2 = { {9,6,6}, {6,8,3}, {3,4,7} };
        int [][] ar3 = { {7,2,5}, {1,4,2}, {6,8,6} };   

        somaMatriz teste = new somaMatriz();

        for (int i = 0; i < 10; i++) {
            System.out.println(teste.matriz(ar1, ar2));

            System.out.println(teste.matriz(ar2, ar3));


        } 
    }

}