[ Java 代碼範本 ] Java Set operation - Union/Intersect/Complement

Preface:
因為在 Java 提供的 Set 介面中並沒有我需要的集合操作, 所以就自己建立類別 SetOP 來處理:
- Unions (連集)
集合 S1 與 集合 S2 進行 Union 後 (S1 ∪ S2), 在操作完成後產生的 集合 會包含所有 S1 與 S2 的所有元素. 簡單範例如下:

- {1, 2} ∪ {red, white} ={1, 2, red, white}.
- {1, 2, green} ∪ {red, white, green} ={1, 2, red, white, green}.
- {1, 2} ∪ {1, 2} = {1, 2}.

- Intersections (交集)
集合 S1 與 集合 S2 進行 Intersection (S1 ∩ S2), 在操作完成後產生的 集合 中的元素會同時出現在 集合 S1 與 S2 中. 簡單範例如下:

- {1, 2} ∩ {red, white} = ∅.
- {1, 2, green} ∩ {red, white, green} = {green}.
- {1, 2} ∩ {1, 2} = {1, 2}.

- Complements (差集)
集合 S1 與 集合 S2 進行 Complement (S1 \ S2 或 S1 - S2), 在操作完成後產生的 集合 中的元素是 集合 S1 中所有元素但不包括出現在 集合 S2 中的那些元素. 簡單範例如下:

- {1, 2} \ {red, white} = {1, 2}.
- {1, 2, green} \ {red, white, green} = {1, 2}.
- {1, 2} \ {1, 2} = ∅.
- {1, 2, 3, 4} \ {1, 3} = {2, 4}.

Implementation:
- Class SetOP

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1. package flib.util;  
2.   
3. import java.util.HashSet;  
4. import java.util.Iterator;  
5. import java.util.Set;  
6.   
7. public class SetOP {  
8.     /** 
9.      * BD: Two sets can also be "subtracted". The relative complement of B in A (also called the set-theoretic difference of A and B),  
10.      *     denoted by A \ B (or A − B), is the set of all elements that are members of A but not members of B.  
11.      *     Note that it is valid to "subtract" members of a set that are not in the set, such as removing the element green from  
12.      *     the set {1, 2, 3}; doing so has no effect. 
13.      * REF: http://en.wikipedia.org/wiki/Set_(mathematics)#Complements 
14.      * @param sa 
15.      * @param sb 
16.      * @return sa - sb 
17.      */  
18.     public Set DIFF(Set sa, Set sb)  
19.     {  
20.         Set s1 = UNION(sa,sb);  
21.         Set s2 = INTERSECT(sa,sb);  
22.         s1.removeAll(s2);  
23.         return s1;  
24.     }  
25.       
26.     /** 
27.      * BD: Two sets can also be "subtracted". The relative complement of B in A (also called the set-theoretic difference of A and B),  
28.      *     denoted by A \ B (or A − B), is the set of all elements that are members of A but not members of B.  
29.      *     Note that it is valid to "subtract" members of a set that are not in the set, such as removing the element green from  
30.      *     the set {1, 2, 3}; doing so has no effect. 
31.      * REF: http://en.wikipedia.org/wiki/Set_(mathematics)#Complements 
32.      * @param sa 
33.      * @param sb 
34.      * @return sa - sb 
35.      */  
36.     public Set COMPLEMENT(Set sa, Set sb)  
37.     {  
38.         return DIFF(sa,sb);  
39.     }  
40.       
41.     /** 
42.      * BD: A new set can also be constructed by determining which members two sets have "in common".  
43.      *     The intersection of A and B, denoted by A ∩ B, is the set of all things that are members of both A and B.  
44.      *     If A ∩ B = ∅, then A and B are said to be disjoint. 
45.      * REF: http://en.wikipedia.org/wiki/Set_(mathematics)#Intersections 
46.      * @param sa 
47.      * @param sb 
48.      * @return sa ∩ sb 
49.      */  
50.     public Set INTERSECT(Set sa, Set sb)  
51.     {  
52.         Set s =  new HashSet();         
53.         if(sa.size()>sb.size())  
54.         {  
55.             s.addAll(sa);  
56.             s.retainAll(sb);  
57.         }  
58.         else  
59.         {  
60.             s.addAll(sb);  
61.             s.retainAll(sa);  
62.         }  
63.         return s;  
64.     }  
65.       
66.     /** 
67.      * BD: Two sets can be "added" together. The union of A and B, denoted by A ∪ B,  
68.      *     is the set of all things that are members of either A or B. 
69.      * REF: http://en.wikipedia.org/wiki/Set_(mathematics)#Unions 
70.      * @param sa 
71.      * @param sb 
72.      * @return sa ∪ sb 
73.      */  
74.     public Set UNION(Set sa, Set sb)  
75.     {  
76.         Set s =  new HashSet();         
77.         if(sa.size()>sb.size())  
78.         {  
79.             s.addAll(sa);  
80.             s.addAll(sb);  
81.         }  
82.         else  
83.         {  
84.             s.addAll(sb);  
85.             s.addAll(sa);  
86.         }  
87.         return s;  
88.     }  
89.       
90.     public void ADD(Set set, E...elms)  
91.     {  
92.         for(E e:elms) set.add(e);  
93.     }  
94.       
95.     public String PrintSet(Set set)  
96.     {  
97.         StringBuffer strBuf = new StringBuffer("[");  
98.         Iterator iter = set.iterator();  
99.         E s = null;  
100.         while(iter.hasNext())  
101.         {  
102.             if(s!=null) strBuf.append(",");  
103.             strBuf.append(String.format("%s", s=iter.next()));  
104.         }  
105.         strBuf.append("]");  
106.         return strBuf.toString();  
107.     }  
108. }  

Usage example:

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1. public static void main(String args[])  
2. {  
3.     Set sa = new HashSet();  
4.     Set sb = new HashSet();  
5.     SetOP sop = new SetOP();  
6.     sop.ADD(sa, 1,2,3,4);  
7.     sop.ADD(sb, 3,4,5,6);  
8.     Set so = null;  
9.     System.out.printf("\t[Info] Set sa: %s\n", sop.PrintSet(sa));  
10.     System.out.printf("\t[Info] Set sb: %s\n", sop.PrintSet(sb));  
11.       
12.     System.out.printf("\t[Info] Union of sa,sb: ");  
13.     so = sop.UNION(sa, sb);  
14.     if(so.size()==0) System.out.printf("\t[]\n");  
15.     else  
16.     {  
17.         Integer elms[] = new Integer[so.size()];  
18.         so.toArray(elms);  
19.         System.out.printf(" [%d", elms[0]);  
20.         for(int i=1; i",%d", elms[i]);  
21.         System.out.println("]");  
22.     }  
23.     System.out.printf("\t[Info] Difference of sa,sb: ");  
24.     so = sop.DIFF(sa, sb);  
25.     if(so.size()==0) System.out.printf(" []\n");  
26.     else  
27.     {  
28.         Integer elms[] = new Integer[so.size()];  
29.         so.toArray(elms);  
30.         System.out.printf(" [%d", elms[0]);  
31.         for(int i=1; i",%d", elms[i]);  
32.         System.out.println("]");  
33.     }  
34.     System.out.printf("\t[Info] Intersection of sa,sb: ");  
35.     so = sop.INTERSECT(sa, sb);  
36.     if(so.size()==0) System.out.printf(" []\n");  
37.     else  
38.     {  
39.         Integer elms[] = new Integer[so.size()];  
40.         so.toArray(elms);  
41.         System.out.printf(" [%d", elms[0]);  
42.         for(int i=1; i",%d", elms[i]);  
43.         System.out.println("]");  
44.     }  
45. }  

執行結果:

[Info] Set sa: [1,2,3,4]
[Info] Set sb: [3,4,5,6]
[Info] Union of sa,sb: [1,2,3,4,5,6]
[Info] Difference of sa,sb: [1,2,5,6]
[Info] Intersection of sa,sb: [3,4]

This message was edited 12 times. Last update was at 14/05/2013 15:27:46