java中TreeSet的Comparator比较器的三种使用方法

java中treeset使用Comparator进行比较的三种方法

1.让元素具备比较性。

比如我们比较两个人。我们定义一个person类，并且实现Comparable接口

例：

public class Person implements Comparable{

private int age;

private String name;

public Person(){}

public Person(int age, String name) {
this.age = age;
this.name = name;
}

public int getAge() {
return age;
}

public String getName() {
return name;
}

public void setAge(int age) {
this.age = age;
}
public void setName(String name) {
this.name = name;
}

@Override
public int compareTo(Object o) {
if (!(o instanceof Person))
throw new RuntimeException("不是人对象");
Person p = (Person) o;
if (this.age > p.age)
return 1;
if (this.age == p.age){
return this.name.compareTo(p.name);
}
return -1;
}

}

2.第二种是写个类实现Comparator接口

例：

class myComparator implements Comparator{

@Override
public int compare(Object o1, Object o2) {
Person p1 = (Person) o1;
Person p2 = (Person) o2;

int num = p1.getName().compareTo(p2.getName());
// 0的话是两个相同，进行下一个属性比较
if (num == 0){
return new Integer(p1.getAge()).compareTo(new Integer(p2.getAge()));
}

return num;
}
}

然后在new Set的时候放进去。如

TreeSet ts = new TreeSet(new myComparator());

3.第三种写内名内部类方法如：

TreeSet ts = new TreeSet(new Comparator() {
@Override
public int compare(Object o1, Object o2) {
Person p1 = (Person) o1;
Person p2 = (Person) o2;

int num = p1.getName().compareTo(p2.getName());

if (num == 0){
return new Integer(p1.getAge()).compareTo(new Integer(p2.getAge()));
}

return num;

}
});