Subtracting one arrayList from another arrayList

Question

I have two arrayLists and I am trying to "subtract" one arrayList from another. For example, if I have one arrayList [1,2,3] and I am trying to subtract [0, 2, 4] the resulting arrayList should be [1,3].

List<Integer> a = new ArrayList<>(Arrays.asList(1, 2, 3)); List<Integer> b = Arrays.asList(0, 2, 4); subtract(a,b) // should return [1,3] 

Here is my code.

//returns a new IntSet after subtracting a from b // .minus().toString() ArrayList<Integer> minusArray = new ArrayList<Integer>();      minusArray.addAll(array1);      for(int i =0; i< minusArray.size(); i++){         for(int j = 0; j < array2.size(); j++){             if(minusArray.get(i).equals(array2.get(j))){                 minusArray.remove(i);                 if(i == 0){                     ;                 }                 else if(j == 0){                     ;                 }                 else{                     i = 0;                     j = 0;                 }             }             else{}         }     }  return minusArray; 

My code works in some cases, like if arrayList1 = [4,6] and arrayList2 = [6] it will will give me a result of [4]. But if I try something like [1,2,4] and [0,4,8]

I get this exception:

java.lang.IndexOutOfBoundsException: Index: 2, Size: 2     at java.util.ArrayList.rangeCheck(Unknown Source)     at java.util.ArrayList.get(Unknown Source)     at IntSet.minus(IntSet.java:119)     at IntSetDriver.main(IntSetDriver.java:62) 

Here is the code I have come up with. I have done test runs through it and to me I think it should work. The user inputs these arrayLists and they are presorted, I also do not know Hash or big-O.

ArrayList<Integer> minusArray = new ArrayList<Integer>();      minusArray.addAll(array1);      for(int i =0; i< minusArray.size(); i++){         for(int j = 0; j < array2.size(); j++){             if(minusArray.get(i).equals(array2.get(j))){                 minusArray.remove(i);             }             else{}         }     }  return minusArray; 

Answer 1

Is there some reason you can't simply use List.removeAll(List)?

    List<Integer> one = new ArrayList<Integer>();     one.add(1);     one.add(2);     one.add(3);     List<Integer> two = new ArrayList<Integer>();     two.add(0);     two.add(2);     two.add(4);     one.removeAll(two);     System.out.println(one);      result: "[1, 3]"