Question

我有兴趣问题。这是一个抽象类，将由子类扩展。在抽象类中，有以下方法：

public abstract class MyAbstractClass {
    protected List<MyObject> findSpecificObjects(List<MyObject> objectsToSelectFrom, List<MyObject> objectsToCompare) {
        List<MyObject> selected = new ArrayList<MyObject>();
        //there I need to select elements from objectsToSelectFrom
        //using MyComparatorAnalogue with objectsToCompare
        return selected;
    }

    protected class MyComparatorAnalogue implements ??? {
        /*this comparator analogue should have an access to objectsToCompare
        it must select elements from objectsToSelectFrom with property myProperty=someValue, where someValue - value that no one element from objectsToCompare have in the same property myProperty
        */
    }
}

我为什么要这么奇怪地做 - 因为我需要能够在子类中覆盖MyComparator。有什么方法可以做我想做的事吗？我查看了Apache Commons Collections，但在这种情况下找不到任何可以帮助我的东西。

例如：

objectsToSelectFrom = {[key=Michael,value=23],[key=Luis,value=44],[key=Andrew,value=26]}
objectsToCompare = {[key=John,value=23],[key=Luis,value=44]}

假设myProperty value属性MyComparatorAnalogue应选择[key=Andrew,value=26]元素。

希望我把它描述为accessibily。感谢。

Answer 1

使用Java 8和流，你可以做这样的事情。

    List<MyObject> l = new ArrayList<>();
    l.add(new MyObject("foo", "FOO"));
    l.add(new MyObject("bar", "BAR"));
    l.add(new MyObject("baz", "BAZ"));

    List<MyObject> whitelist = new ArrayList<>();
    whitelist.add(new MyObject("other bar", "BAR"));

    Predicate<? super MyObject> inWhitelist = (MyObject o) -> {
        return whitelist.stream().anyMatch((p) ->
          o.getValue().equals(p.getValue()));
    };

    List<MyObject> filtered =
      l.stream().filter(inWhitelist).collect(Collectors.toList());

现在filtered包含的MyObject("bar", "BAR")与value具有相同的MyObject("other bar", "BAR")。

Java - 非匿名Comparator类似于从集合中选择元素

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