如下所示：这是一个List,其中每一行是一个object. 我想对这个List进行分组，第一关键字是A列 。第二关键字B列。
A B C
ANN1 off1 null
ANN2 off2 V1
ANN2 off2 V2
ANN3 off2 V1
ANN3 off2 V2
ANN3 off3 V3
进行分组后显示的效果如下：
ANN1#
off1
ANN2#
off2
V1
V2
ANN3#
off2
V1
V2
v3
------解决方案--------------------
用List或/和Map的嵌套就可以解决。
比如一个Map的key是你的A列，Map的value是另一个Map；嵌套的这个Map的key是你的B列或者C列，value是空。如果你需要把B列、C列区别看来，那就做个Pair对象作为第一个Map的value，Pair里放两个Map，一个对应B列，一个对应C列。
以上只是一个思路，有很多方式可以解决。
------解决方案--------------------
学习一下 顶
------解决方案--------------------
[color=#99CCFF]
- Java code
package sunflowerbbs.oicp.net;import java.util.ArrayList;import java.util.Collections;import java.util.Iterator;public class GroupByKey { private static class Record implements Comparable<Record>, Cloneable { private String _A; private String _B; private String _C; public Record(String _a, String _b, String _c) { _A = _a; _B = _b; _C = _c; } private Record() { } public int compareTo(Record record) { int result = this._A.compareTo(record._A); if (result != 0) { return result; } else { return this._B.compareTo(record._B); } } public Object clone() { Record record = new Record(); record._A = new String(this._A); record._B = new String(this._B); record._C = this._C != null ? new String(this._C) : null; return record; } } public static void main(String[] args) { Record r1, r2, r3, r4, r5, r6, r7; r1 = new Record("A2", "B3", "C3"); r2 = new Record("A3", "B4", "C5"); r3 = new Record("A2", "B3", "C2"); r4 = new Record("A1", "B1", null); r5 = new Record("A2", "B3", "C4"); r6 = new Record("A1", "B2", "C1"); r7 = new Record("A3", "B4", "C7"); ArrayList<Record> list = new ArrayList<Record>(); list.add(r1); list.add(r2); list.add(r3); list.add(r4); list.add(r5); list.add(r6); list.add(r7); Collections.<Record> sort(list); Iterator it = list.iterator(); StringBuffer buffA = new StringBuffer(); StringBuffer buffB = new StringBuffer(); StringBuffer buffC = new StringBuffer(); Record prior = (Record) it.next(); buffA.append(prior._A); buffB.append(prior._B); buffC.append(prior._C == null ? "" : " " + prior._C); //chang it by yourself while (it.hasNext()) { Record next = (Record) it.next(); int result1 = prior._A.compareTo(next._A); int result2 = prior._B.compareTo(next._B); if (result1 != 0) { System.out.println(buffA.toString() + "\n " + buffB.toString() + "\n " + buffC.toString() + "\n "); //chang it by yourself buffA = new StringBuffer(next._A); buffB = new StringBuffer(next._B); buffC = new StringBuffer(next._C); } else if (result2 != 0) { buffB.append("\n " + next._B); buffC.append("\n " + next._C); } else { buffC.append("\n " + next._C == null ? "" : next._C); } prior = (Record) next.clone(); if (!it.hasNext()) { if (!buffA.toString().equals(prior._A)) { System.out.println(prior._A + "\n " + prior._B + "\n " + prior._C + "\n "); //chang it by yourself } else { System.out.println(buffA.toString() + "\n " + buffB.toString() + "\n " + buffC.toString() + "\n "); //chang it by yourself } } } }}