Comparing array list of string array

问题

I want to compare two ArrayList of string arrays.

   List<String[]> list1 = new ArrayList<String[]>;
   List<String[]> list2 = new ArrayList<String[]>;

   list1.equals(list2);

This will return false because equals method in ArrayList will do equals on the element.

    ListIterator<E> e1 = listIterator();
    ListIterator<?> e2 = ((List<?>) o).listIterator();
    while (e1.hasNext() && e2.hasNext()) {
        E o1 = e1.next();
        Object o2 = e2.next();
        if (!(o1==null ? o2==null : o1.equals(o2)))
            return false;
    }
    return !(e1.hasNext() || e2.hasNext());

If you do equals on array, it will check reference equality. Is there anyway we can use list1.equals(list2) instead of checking each element in array list.

回答1:

You can not do it by using equals. Instead of doing equals, you can do retainAll(). You can just write a small function, say isEqual() and use this where you are using equals. You need to convert your array as list and pass it to this function.

{ 
  ListIterator<E> e1 = listIterator();
  ListIterator<?> e2 = ((List<?>) o).listIterator();
  while (e1.hasNext() && e2.hasNext()) {
      E o1 = e1.next();
      Object o2 = e2.next();
      if (!(o1==null ? o2==null : isEqual(Arrays.alList(o1),Arrays.asList(o2))))
        return false;
   }
   return !(e1.hasNext() || e2.hasNext()); 
}

     boolean isEqual(List list1, List list2){

          int originalSize = list1.size();
          list1.retainAll(list2); 
          // list1 will retain all the elements that are present in list2
          // if list1 has all the elements that are present in list2, present list1 size will be equal to `original size`
          if(list1.size() == originlaSize){
              returns true;
          }else{
              return false;
          }

     }

回答2:

You can use list1.equals(list2) if you change from List<String[]> to List<List<String>>.

public static void main(String[] args) throws Exception {
    List<List<String>> list1 = new ArrayList() {{
       add(new ArrayList(Arrays.asList("a", "b", "c"))); 
       add(new ArrayList(Arrays.asList("d", "e", "f")));
       add(new ArrayList(Arrays.asList("g", "h", "i")));
    }};
    List<List<String>> list2 = new ArrayList()  {{
       add(new ArrayList(Arrays.asList("a", "b", "c"))); 
       add(new ArrayList(Arrays.asList("d", "e", "f")));
       add(new ArrayList(Arrays.asList("g", "h", "i")));
    }};

    System.out.println(list1);
    System.out.println(list2);
    System.out.println(list1.equals(list2));
}

Results:

[[a, b, c], [d, e, f], [g, h, i]]
[[a, b, c], [d, e, f], [g, h, i]]
true

Otherwise, you're probably looking something along the lines of:

public static void main(String[] args) throws Exception {
    List<String[]> list1 = new ArrayList() {{
       add(new String[] {"a", "b", "c"}); 
       add(new String[] {"d", "e", "f"});
       add(new String[] {"g", "h", "i"});
    }};
    List<String[]> list2 = new ArrayList()  {{
       add(new String[] {"a", "b", "c"}); 
       add(new String[] {"d", "e", "f"});
       add(new String[] {"g", "h", "i"});
    }};

    System.out.println(listsEqual(list1, list2));
}

public static boolean listsEqual(List<String[]> list1, List<String[]> list2) {
    if (list1.size() != list2.size()) {
        return false;
    }

    for (int i = 0; i < list1.size(); i++) {
        if (!Arrays.equals(list1.get(i), list2.get(i))){
            return false;
        }
    }
    return true;
}

Results:

true

回答3:

Make a simple wrapper for the array class.

private String[] array;
public ArrayWrapper(String[] array) {
    this.array = array;
}

Override equals(Object obj) to use Arrays.equals(array, (String[]) obj) and just hashCode() is just array.hashCode().

来源：https://stackoverflow.com/questions/31644416/comparing-array-list-of-string-array

标签

java

arrays

arraylist

equals