comparable 接口：
1. 问题：java.util.Collections 类中的方法 Collections.sort(List list) 是根据什么确定容器中对象的“大小”顺序的？
2. java 中所有可以“排序”的类都实现了 java.lang.comparable 接口，Comparable 接口中只有一个方法：
public int compareTo(Object obj)：在该方法中，
返回 0， 表示 this == obj;
返回 正数，表示 this > obj;
返回 负数，表示 this < obj;
3. 实现了 comparable 接口的类通过实现 compareTo 方法从而确定该对象的排序方式.
Demo_1:
class MyName implements Comparable<MyName>{
private int age;
public MyName(int age) {
this.age = age;
}
@Override
public int compareTo(MyName mn) {
if(this.age>mn.age){
return 1;
}else if(this.age<mn.age){
return -1;
}else {
return 0;
}
}
}
public class Test {
public static void main(String[] args) {
MyName m1 = new MyName(12);
MyName m2 = new MyName(25);
System.out.println(m1.compareTo(m2)); // 输出：-1
}
}
Demo_2:
import java.util.*;
class Name implements Comparable<Name>{
private String firstName, lastName;
public Name(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
public String getFirstName(){
return firstName;
}
public String getLastName(){
return lastName;
}
@Override
public String toString() {
return firstName+" "+lastName;
}
@Override
public boolean equals(Object obj) {
if(obj instanceof Name){
Name name = (Name)obj;
return (getFirstName().equals(name.firstName)) && (getLastName().equals(name.lastName));
}
return super.equals(obj);
}
@Override
public int hashCode() {
return firstName.hashCode();
}
public int compareTo(Name objj) {
int cmpResult = lastName.compareTo(objj.lastName);
return cmpResult !=0 ? cmpResult:firstName.compareTo(firstName);
}
}
class Test {
public static void main(String[] args) {
LinkedList<Name> ln = new LinkedList<Name>();
ln.add(new Name("song","bo"));
ln.add(new Name("song","qi"));
ln.add(new Name("song","ting"));
ln.add(new Name("liu","bo"));
ln.add(new Name("fang","qi"));
ln.add(new Name("shang","qi"));
ln.add(new Name("zhu","ting"));
System.out.println(ln); // 输出：
Collections.sort(ln);
System.out.println(ln); // 输出：
}
}
// 第1次输出： [song bo, song qi, song ting, liu bo, fang qi, shang qi, zhu ting]
// 第2次输出： [song bo, liu bo, song qi, fang qi, shang qi, song ting, zhu ting]