我們之前學(xué)習(xí)的類都無法對元素自動排序情屹，java設(shè)置這個類能夠?qū)Υ嬖诩现械脑刈詣优判颍琓reeSet類的底層使用的是二叉樹結(jié)構(gòu)褐隆。在儲存對象時會根據(jù)對象的比較功能豆村，確定對象的大小，從而確定該對象在二叉樹中的位置脸秽。
import java.util.Iterator;
import java.util.TreeSet;
public class TreeSetDemo {
public static void main(String[] args) {
TreeSet ts=new TreeSet();
ts.add("aaaa");
ts.add("bbbb");
ts.add("cccc");
ts.add("dddd");
for (Iterator iterator = ts.descendingIterator(); iterator.hasNext();) {
System.out.println(iterator.next());
}
}
}
底層TreeSet類在對對像進(jìn)行排序時其實是將對象強(qiáng)轉(zhuǎn)成cmparable儒老，然后通過comparableTo方法進(jìn)行比較大小，從而確定位置记餐。
java中規(guī)定要想某個類具有比較功能贷盲，就要實現(xiàn)comparable接口。所以當(dāng)TreeSet類存放自定義類時剥扣，該類要實現(xiàn)comparable接口。
用TreeSet類存放自定義對象：
import java.util.Iterator;
import java.util.TreeSet;
class People implements Comparable {
private String name;
private int age;
public People(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "People [name=" + name + ", age=" + age + "]";
}
@Override
public int compareTo(Object o) {
// TODO Auto-generated method stub
People p = (People) o;
return this.age - p.age;
}
}
public class TreeSetDemo {
public static void main(String[] args) {
TreeSet ts = new TreeSet();
ts.add(new People("aaaa", 128));
ts.add(new People("m", 122));
ts.add(new People("aaaa", 122));
ts.add(new People("aana", 11));
for (Iterator iterator = ts.descendingIterator(); iterator.hasNext();) {
System.out.println(iterator.next());
}
}
}
