org.apache.commons.collections.CollectionUtils

１.集合的交集、补集、差集、并集

 

List<String> a = Arrays.asList(new String[] { "1", "2", "3", "4","4", "8" });
List<String> b = Arrays.asList(new String[] { "3", "4", "5", "6", "7" });

 

List<String> union = (List<String>) CollectionUtils.union(a, b);// 并集
List<String> intersection = (List<String>)CollectionUtils.intersection(a, b);// 交集
List<String> disjunction = (List<String>)CollectionUtils.disjunction(a, b);// 交集的补集
List<String> subtract =(List<String>) CollectionUtils.subtract(a, b);// 集合相减

Collections.sort(union);
Collections.sort(intersection);
Collections.sort(disjunction);
Collections.sort(subtract);

System.out.println("a:" + a.toString());
System.out.println("b:" + b.toString());
System.out.println("union:" + union.toString());
System.out.println("intersection:" + intersection.toString());
System.out.println("disjunction:" + disjunction.toString());
System.out.println("subtract:" + subtract.toString());

 

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结果如下：

a:[1, 2, 3, 4, 4, 8]
b:[3, 4, 5, 6, 7]
union:[1, 2, 3, 4, 4, 5, 6, 7, 8]
intersection:[3, 4]
disjunction:[1, 2, 4, 5, 6, 7, 8]
subtract:[1, 2, 4, 8]

 

2.有一个Ｌist<T>的集合t1，Ｔ的属性有a和b,现在要将t1集合中对象属性为a提出来组成一个集合，可以使用以下方法

CollectionUtils.collect(t1, new BeanToPropertyValueTransformer("a")

 

 

Student s = new Student();
s.setName("张三");
s.setAge(13);

Student s1 = new Student();
s1.setName("李四");
s1.setAge(11);

List<Student> list = new ArrayList<Student>();
list.add(s);
list.add(s1);

List<Integer> list2 = (List<Integer>)CollectionUtils.collect(list, new BeanToPropertyValueTransformer("age"));
for (Integer name : list2) {
System.out.println(name);
}

 

 

结果如下：

13
11