a simple program

Hi all! I am trying to create a table of values with the last row blank so that when the user clicks at the button('sum' or 'average') it will display the result in the last row.
whats wrong with this?it says i cant assign values to the array in the array declaration..??

import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;

public class array extends Applet implements ActionListener
{
private Button sum, average;
int total=0;
int[][] a=new int[4][4];

//int []a;
//int []b;
//int[] a= new int[4];
//int[] b= new int[4];
//int[] c= new int[4];
//total = sum(a);
a[0][0]=1;
a[1][0]=2;
a[2][0]=3;
a[3][0]=0;
a[1][1]=4;
a[2][1]=5;
a[3][1]=6;
a[4][1]=0;
a[0][2]=7;
a[1][2]=8;
a[2][2]=9;
a[3][2]=0;
a[0][3]=10;
a[1][3]=11;
a[2][3]=12;
a[3][3]=0;
//a={1,2,3,0};
//a[0]=1;
//a[1]=1;
//a[2]=1;
//a[3]=0;
//b={5,6,7,0};
//b[0]=1;
//b[1]=1;
//b[2]=1;
//b[3]=0;
//Button sum;
//Button average;

sum= new Button("Sum"); //supplying the 2 buttons
add(sum);
sum.addActionListener(this);

average= new Button("Average");
add(average);
sum.addActionListener(this);

for (int i = 0; i < a.length; i++){
System.out.println( a[i] );
}
public void paint (Graphics g){
public int sum(int[][] a){
total=0;
for(int row=0;row<4;row++){ //to get the sum of the row
for(int col=0;col<4;col++){
total=total+a[row][col];
return total;
//g.drawString("total: " +total,a[3][3]
}
}
}

public int average(int[][] a){
for (int row=0;row<4;row++){
for(int col=0;col<4;col++){
int total=total+a[row][col];
int average (total/3);
return average;
}
}
}

}