CollectionUtils各种集合工具方法

最新推荐文章于 2025-02-16 10:55:44 发布

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最新推荐文章于 2025-02-16 10:55:44 发布

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本文详细介绍了Java中CollectionUtils的各种集合操作，包括并集、交集、交集的补集（析取）、差集（扣除）、判断集合是否为空以及验证集合是否相等。通过这些工具方法，可以更方便地处理Java集合类对象。

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1, 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]
}

2, 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]
}

3, 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]
}

4, 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arrayB
    System.out.println(ArrayUtils.toString(CollectionUtils.subtract(listA, listB)));
    //[A, C, E]
 
}

5, 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));   //true
    System.out.println(CollectionUtils.isEmpty(second));   //true
    System.out.println(CollectionUtils.isEmpty(boy));   //false
 
    //判断集合是否不为空
    System.out.println(CollectionUtils.isNotEmpty(first));   //false
    System.out.println(CollectionUtils.isNotEmpty(second));   //false
    System.out.println(CollectionUtils.isNotEmpty(boy));   //true
}

6, 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));   //true
System.out.println(CollectionUtils.isEqualCollection(first,boy1));   //false
System.out.println(CollectionUtils.isEqualCollection(boy1,boy2));   //false

List<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
}

7, 不可修改的集合

@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);
}