Android笔记：java 集合的 交叉并合

 原文地址

public class SetOpt { 

    public List intersect(List ls, List ls2) { 
        List list = new ArrayList(Arrays.asList(new Object[ls.size()])); 
        Collections.copy(list, ls); 
        list.retainAll(ls2); 
        return list; 
    } 

    public List union(List ls, List ls2) { 
        List list = new ArrayList(Arrays.asList(new Object[ls.size()])); 
        Collections.copy(list, ls); 
       list.addAll(ls2); 
        return list; 
    } 

    public List diff(List ls, List ls2) { 
        List list = new ArrayList(Arrays.asList(new Object[ls.size()])); 
        Collections.copy(list, ls); 
        list.removeAll(ls2); 
        return list; 
    } 
    public static void main(String[] args) { 
        SetOpt opt = new SetOpt(); 
        List l1 = new ArrayList(); 
        l1.add(1); 
        l1.add(2); 
        l1.add(3); 
        l1.add(4); 
        List l2 = new ArrayList(); 
        l2.add(3); 
        l2.add(4); 
        l2.add(5); 
        l2.add(6); 
        List intersectList = opt.intersect(l1, l2); 
        System.out.println("交集："); 
        for (int i = 0; i < intersectList.size(); i++) { 
            System.out.print(intersectList.get(i) + " "); 
        } 
        System.out.println(); 
        List unionList = opt.union(l1, l2); 
        System.out.println("并集："); 
        for (int i = 0; i < unionList.size(); i++) { 
            System.out.print(unionList.get(i) + " "); 
        } 
        System.out.println(); 
        List diffList = opt.diff(l1, l2); 
        System.out.println("差集："); 
        for (int i = 0; i < diffList.size(); i++) { 
            System.out.print(diffList.get(i) + " "); 
        } 
        System.out.println(); 
    } 

}

 

在进行两个集合（操作集合和被操作集合）交、并、差操作时，一定要先将操作集合拷贝一份，以拷贝的集合作为操作集合来进行运算。否则，将改变原来操作集合的内容