java TreeMap 排序 与 TreeSet 排序

TreeMap:

package com;import java.util.Comparator;import java.util.TreeMap;public class Test5 {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubTreeMap<String, String> tree = new TreeMap<String, String>(new Comparator<Object>() {@Overridepublic int compare(Object o1, Object o2) {// TODO Auto-generated method stubif(o1 == null || o2 == null){return 0;}return o1.toString().compareTo(o2.toString());}});tree.put("k", "1");tree.put("ba", "2");tree.put("z", "3");tree.put("d", "4");tree.put("e", "5");tree.put("an", "6");tree.put("c", "7");for(String str : tree.keySet()){System.out.println(str);}}}

经测试默认是按照 KEY 进行排序的。

但是可以写对象比较器，进行自定义排序。

TreeSet : 自定义倒序排序，默认按照正序排序，1,2,3,4,5,6

package com;import java.util.Comparator;import java.util.TreeSet;public class Test6 {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubTreeSet<Object> tree  = new TreeSet<Object>(new Comparator<Object>() {@Overridepublic int compare(Object o1, Object o2) {// TODO Auto-generated method stubif(o1 == null || o2 == null){return 0;}if(Integer.parseInt(o1.toString()) > Integer.parseInt(o2.toString())){return -1;}else if(Integer.parseInt(o1.toString()) < Integer.parseInt(o2.toString())){return 1;}else{return 0;}}});tree.add(4);tree.add(5);tree.add(6);tree.add(1);tree.add(2);tree.add(3);for(Object o : tree){System.out.println(o);}}}