CollectionUtils工具类常用方法小结

CollectionUtils在真实项目中，是一个非常好用的工具类，使用非常频繁。它可以使代码更加简洁和安全。刚好在工作中利用这个工具类重构代码，顺便总结下分享分享:

并集

@Test
public void testUnion(){String[] arrayA = new String[] { "A", "B", "C", "D", "E", "F" };  String[] arrayB = new String[] { "B", "D", "F", "G", "H", "K" };List<String> listA = Arrays.asList(arrayA);List<String> listB = Arrays.asList(arrayB);//2个数组取并集 System.out.println(ArrayUtils.toString(CollectionUtils.union(listA, listB)));//[A, B, C, D, E, F, G, H, K]
}

交集

@Test
public void testIntersection(){String[] arrayA = new String[] { "A", "B", "C", "D", "E", "F" };  String[] arrayB = new String[] { "B", "D", "F", "G", "H", "K" };List<String> listA = Arrays.asList(arrayA);List<String> listB = Arrays.asList(arrayB);//2个数组取交集 System.out.println(ArrayUtils.toString(CollectionUtils.intersection(listA, listB)));//[B, D, F]}

交集的补集（析取）

@Test
public void testDisjunction(){String[] arrayA = new String[] { "A", "B", "C", "D", "E", "F" };  String[] arrayB = new String[] { "B", "D", "F", "G", "H", "K" };List<String> listA = Arrays.asList(arrayA);List<String> listB = Arrays.asList(arrayB);//2个数组取交集 的补集System.out.println(ArrayUtils.toString(CollectionUtils.disjunction(listA, listB)));//[A, C, E, G, H, K]
}

差集（扣除）

@Test
public void testSubtract(){String[] arrayA = new String[] { "A", "B", "C", "D", "E", "F" };  String[] arrayB = new String[] { "B", "D", "F", "G", "H", "K" };List<String> listA = Arrays.asList(arrayA);List<String> listB = Arrays.asList(arrayB);//arrayA扣除arrayBSystem.out.println(ArrayUtils.toString(CollectionUtils.subtract(listA, listB)));//[A, C, E]}

集合是否为空

@Test
public void testIsEmpty(){class Person{}class Girl extends Person{}List<Integer> first = new ArrayList<>();List<Integer> second = null;List<Person> boy = new ArrayList<>();//每个男孩心里都装着一个女孩boy.add(new Girl());//判断集合是否为空System.out.println(CollectionUtils.isEmpty(first));   //trueSystem.out.println(CollectionUtils.isEmpty(second));   //trueSystem.out.println(CollectionUtils.isEmpty(boy));   //false//判断集合是否不为空System.out.println(CollectionUtils.isNotEmpty(first));   //falseSystem.out.println(CollectionUtils.isNotEmpty(second));   //falseSystem.out.println(CollectionUtils.isNotEmpty(boy));   //true
}

集合是否相等

@Test
public void testIsEqual(){class Person{}class Girl extends Person{}List<Integer> first = new ArrayList<>();List<Integer> second = new ArrayList<>();first.add(1);first.add(2);second.add(2);second.add(1);Girl goldGirl = new Girl();List<Person> boy1 = new ArrayList<>();//每个男孩心里都装着一个女孩boy1.add(new Girl());List<Person> boy2 = new ArrayList<>();//每个男孩心里都装着一个女孩boy2.add(new Girl());//比较两集合值System.out.println(CollectionUtils.isEqualCollection(first,second));   //trueSystem.out.println(CollectionUtils.isEqualCollection(first,boy1));   //falseSystem.out.println(CollectionUtils.isEqualCollection(boy1,boy2));   //falseList<Person> boy3 = new ArrayList<>();//每个男孩心里都装着一个女孩boy3.add(goldGirl);List<Person> boy4 = new ArrayList<>();boy4.add(goldGirl);System.out.println(CollectionUtils.isEqualCollection(boy3,boy4));   //true
}

不可修改的集合

我们对c进行操作，s也同样获得了和c相同的内容，这样就可以避免其他人员修改这个s对象。有时候需要对它进行保护，避免返回结果被人修改。

@Test
public void testUnmodifiableCollection(){Collection<String> c = new ArrayList<>();Collection<String> s = CollectionUtils.unmodifiableCollection(c);c.add("boy");c.add("love");c.add("girl");//! s.add("have a error");System.out.println(s);
}