Java中的Set操作

首先看一個例子：

Set operations: union（並集）, intersection（交集）,asymetric difference（非對稱差集）, symmetric difference（對稱差集）, is subset（子集）, is superset（超集）

import java.util.Set; import java.util.TreeSet; public class SetTest { public static <T> Set<T> union(Set<T> setA, Set<T> setB) { Set<T> tmp = new TreeSet<T>(setA); tmp.addAll(setB); return tmp; } public static <T> Set<T> intersection(Set<T> setA, Set<T> setB) { Set<T> tmp = new TreeSet<T>(); for (T x : setA) if (setB.contains(x)) tmp.add(x); return tmp; } public static <T> Set<T> intersection2(Set<T> setA, Set<T> setB) { Set<T> tmp = new TreeSet<T>(setA); tmp.retainAll(setB); return tmp; } public static <T> Set<T> difference(Set<T> setA, Set<T> setB) { Set<T> tmp = new TreeSet<T>(setA); tmp.removeAll(setB); return tmp; } public static <T> Set<T> symDifference(Set<T> setA, Set<T> setB) { Set<T> tmpA; Set<T> tmpB; tmpA = union(setA, setB); tmpB = intersection(setA, setB); return difference(tmpA, tmpB); } public static <T> boolean isSubset(Set<T> setA, Set<T> setB) { return setB.containsAll(setA); } public static <T> boolean isSuperset(Set<T> setA, Set<T> setB) { return setA.containsAll(setB); } public static void main(String args[]) { TreeSet<Character> set1 = new TreeSet<Character>(); TreeSet<Character> set2 = new TreeSet<Character>(); set1.add('A'); set1.add('B'); set1.add('C'); set1.add('D'); set2.add('C'); set2.add('D'); set2.add('E'); set2.add('F'); System.out.println("set1: " + set1); System.out.println("set2: " + set2); System.out.println("Union: " + union(set1, set2)); System.out.println("Intersection: " + intersection(set1, set2)); System.out.println("Intersection2: " + intersection2(set1, set2)); System.out.println("Difference (set1 - set2): " + difference(set1, set2)); System.out.println("Symmetric Difference: " + symDifference(set1, set2)); TreeSet<Character> set3 = new TreeSet<Character>(set1); set3.remove('D'); System.out.println("set3: " + set3); System.out.println("Is set1 a subset of set2? " + isSubset(set1, set3)); System.out.println("Is set1 a superset of set2? " + isSuperset(set1, set3)); System.out.println("Is set3 a subset of set1? " + isSubset(set3, set1)); System.out.println("Is set3 a superset of set1? " + isSuperset(set3, set1)); } }

這裏很重要的是，一些集合操作會修改原始集合，比如addAll，retainAll，removeAll。尤其是你要重複操作原始集合的時候，一定要新建一個集合，new  TreeSet<T> ( orginalSet )。

 

參考：

http://www.java2s.com/Code/Java/Collections-Data-Structure/Set.htm