Java中的Set操作

首先看一个例子：

Set operations: union（并集）, intersection（交集）,asymetric difference（非对称差集）, symmetric difference（对称差集）, 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));
  }
}

这里很重要的是，一些集合操作会修改原始集合，比如addAll，retainAll，removeAll。尤其是你要重复操作原始集合的时候，一定要新建一个集合，new TreeSet<T> ( orginalSet )。

参考：

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