本文主要是介绍CollectionUtils工具类使用指南，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
CollectionUtils提供很多对集合的操作方法，常用的方法如下：
//并集
Collection<String> union = CollectionUtils.union(a, b);
//交集
Collection<String> intersection = CollectionUtils.intersection(a, b);
//交集的补集
Collection<String> disjunction = CollectionUtils.disjunction(a, b);
//集合相减
Collection<String> subtract = CollectionUtils.subtract(a, b);
//判断集合是否为空
Boolean boolean = CollectionUtils.isEmpty(Collection<?> collection);
//判断集合是否不为空
Boolean boolean = CollectionUtils.isNotEmpty(Collection<?> collection);
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);
}
Collections.unmodifiableCollection可以得到一个集合的镜像，它的返回结果是不可直接被改变，否则会提示错误
java.lang.UnsupportedOperationException
at org.apache.commons.collections.collection.UnmodifiableCollection.add(UnmodifiableCollection.java:75)
这篇关于CollectionUtils工具类使用指南的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！
