java.lang.ArrayIndexOutOfBoundsException: Index 20 out of bounds for length 20

Im doing a thing for a thing and I have to "Multiply each element in list2 by its element index number and place the value in array list1." and so my code is

public static void main(String[] args) {        
        int List1 []= {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,};
        int List2 []= {-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1}; 
        int L1= 0;
        int L2= 0;

        for( L2=0 ;L2<List2.length;L2++) {
            List2[L2]= (int) (100*Math.random());
            System.out.print(" "+List2[L2]);
        }//end of list2 for loop

System.out.println("");

        for( L1 = 0;L1<List1.length;L1++)
        {
            List1[L1]= List2[L2]*L2;
            System.out.print(" "+List1[L1]);
        }//end of list1 for loop
)

and it throws this error "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 20 out of bounds for length 20"