TreeSet是Set接口的子類,它可以對元素進行排序,是不同步的,可以保證元素的唯一性:其方式爲通過指定的比較方式對兩個元素進行比較,如果返回值爲0,那麼視爲相同元素,不會再次存儲。
第一種比較方式:
public class Person {
private String name;
private int age;
public Person(String name, int age) {
super();
this.name = name;
this.age = age;
}
public Person() {
super();
}
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;
}
}
import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;
public class TreeSetDemo {
public static void main(String[] args) {
TreeSet ts = new TreeSet(new ComparatorImpl());
/*使用TreeSet參數爲Comparator的構造方法,那麼TreeSet本身具備比較能力,
* 優先級高於元素自身的比較能力。
*/
ts.add(new Person("zhangsan",20));
ts.add(new Person("zhangsan",28));
ts.add(new Person("lisi",21));
ts.add(new Person("lisi",23));
ts.add(new Person("wangwu",22));
ts.add(new Person("wangwu",24));
ts.add(new Person("zhaoliu",23));
ts.add(new Person("zhaoliu",28));
ts.add(new Person("qianqi",24));
ts.add(new Person("qianqi",29));
Iterator it = ts.iterator();
while(it.hasNext()){
Person p = (Person) it.next();
System.out.println("name="+p.getName()+"....age="+p.getAge());
}
}
}
class ComparatorImpl implements Comparator{
//自定義比較器,實現Comparator接口,重寫compare方法。
public int compare(Object o1, Object o2) {
Person p1 = (Person)o1;
Person p2 = (Person)o2;
int temp = p1.getName().compareTo(p2.getName());
//按照名字排序,如果名字相同,就以年齡排序
return (temp==0)?p1.getAge()-p2.getAge():temp;
}
}
第二種比較方式:
public class Student implements Comparable{
/*
* 元素實現Comparable接口,重寫compareTo方法,使得元素
* 自身具備比較能力
*/
private String name;
private int grade;
public Student() {
super();
}
public Student(String name, int grade) {
super();
this.name = name;
this.grade = grade;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getGrade() {
return grade;
}
public void setGrade(int grade) {
this.grade = grade;
}
public int compareTo(Object o) {
Student s = (Student)o;
int temp = this.getName().compareTo(s.getName());
return temp==0?this.getGrade()-s.getGrade():temp;
}
}
import java.util.Iterator;
import java.util.TreeSet;
public class TreeSetDemo2 {
public static void main(String[] args) {
TreeSet ts = new TreeSet();
ts.add(new Student("zhangsan",20));
ts.add(new Student("zhangsan",28));
ts.add(new Student("lisi",21));
ts.add(new Student("lisi",23));
ts.add(new Student("wangwu",22));
ts.add(new Student("wangwu",24));
ts.add(new Student("zhaoliu",23));
ts.add(new Student("zhaoliu",28));
ts.add(new Student("qianqi",24));
ts.add(new Student("qianqi",29));
Iterator it = ts.iterator();
while(it.hasNext()){
Student s = (Student) it.next();
System.out.println("name="+s.getName()+"....grade="+s.getGrade());
}
}
}
如果將方式一中的compare方法改爲return 1,方式二中的compareTo方法也改爲return 1,也就是說忽略元素的屬性,那麼遍歷時會按照添加的順序輸出,同理改爲-1會按照添加的相反的順序輸出。