Android中list集合的排序方法

Collections对List集合中的数据进行排序

有时候需要对集合中的元素按照一定的规则进行排序，这就需要用到

Java中提供的对集合进行操作的工具类Collections，其中的sort方法

先看一个简单的例子：

[java] view plain copy print ?

public static void main(String[] args) {
List nums = new ArrayList();
nums.add(3);
nums.add(5);
nums.add(1);
nums.add(0);
System.out.println(nums);
Collections.sort(nums);
System.out.println(nums);
}

public static void main(String[] args) {    List nums = new ArrayList();        nums.add(3);        nums.add(5);        nums.add(1);        nums.add(0);        System.out.println(nums);        Collections.sort(nums);        System.out.println(nums);}

输出结果：
[3, 5, 1, 0]
[0, 1, 3, 5]

稍微复杂的List里面放一个复杂的对象

[java] view plain copy print ?

package core.java.collection.collections;
public class User implements Comparable{
private int score;
private int age;
public User(int score, int age){
super();
this.score = score;
this.age = age;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public int compareTo(User o) {
int i = this.getAge() - o.getAge();//先按照年龄排序
if(i == 0){
return this.score - o.getScore();//如果年龄相等了再用分数进行排序
}
return i;
}
}
public static void main(String[] args) {
List users = new ArrayList();
users.add(new User(78, 26));
users.add(new User(67, 23));
users.add(new User(34, 56));
users.add(new User(55, 23));
Collections.sort(users);
for(User user : users){
System.out.println(user.getScore() + ”,” + user.getAge());
}
}

package core.java.collection.collections;public class User implements Comparable{    private int score;    private int age;    public User(int score, int age){        super();        this.score = score;        this.age = age;    }    public int getScore() {        return score;    }    public void setScore(int score) {        this.score = score;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    @Override    public int compareTo(User o) {        int i = this.getAge() - o.getAge();//先按照年龄排序        if(i == 0){            return this.score - o.getScore();//如果年龄相等了再用分数进行排序        }        return i;    }}public static void main(String[] args) {        List users = new ArrayList();        users.add(new User(78, 26));        users.add(new User(67, 23));        users.add(new User(34, 56));        users.add(new User(55, 23));        Collections.sort(users);        for(User user : users){            System.out.println(user.getScore() + "," + user.getAge());        }}

输出结果：
55,23
67,23
78,26
34,56
我们会发现sort(List)方法中List中的T必须实现Comparable接口，然后实现
compareTo（）方法，该方法的返回值0代表相等，1表示大于，-1表示小于；为什么
在简单例子中没有看到实现Comparable接口呢？是因为Integer类其实自己已经实现
了Comparable接口，Java已经给我们做好了。

Collections提供的第二种排序方法sort(List list, Comparator<? super T> c)
先看例子：
[java] view plain copy print ?

package core.java.collection.collections;
public class Students {
private int age;
private int score;
public Students(int age, int score){
super();
this.age = age;
this.score = score;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
}
public static void main(String[] args) {
List students = new ArrayList();
students.add(new Students(23, 100));
students.add(new Students(27, 98));
students.add(new Students(29, 99));
students.add(new Students(29, 98));
students.add(new Students(22, 89));
Collections.sort(students, new Comparator() {
@Override
public int compare(Students o1, Students o2) {
int i = o1.getScore() - o2.getScore();
if(i == 0){
return o1.getAge() - o2.getAge();
}
return i;
}
});
for(Students stu : students){
System.out.println(”score:” + stu.getScore() + “:age” + stu.getAge());
}
}

package core.java.collection.collections;public class Students {    private int age;    private int score;    public Students(int age, int score){        super();        this.age = age;        this.score = score;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public int getScore() {        return score;    }    public void setScore(int score) {        this.score = score;    }}public static void main(String[] args) {        List students = new ArrayList();        students.add(new Students(23, 100));        students.add(new Students(27, 98));        students.add(new Students(29, 99));        students.add(new Students(29, 98));        students.add(new Students(22, 89));        Collections.sort(students, new Comparator() {            @Override            public int compare(Students o1, Students o2) {                int i = o1.getScore() - o2.getScore();                if(i == 0){                    return o1.getAge() - o2.getAge();                }                return i;            }        });        for(Students stu : students){            System.out.println("score:" + stu.getScore() + ":age" + stu.getAge());        }}

输出结果：
score:89:age22
score:98:age27
score:98:age29
score:99:age29
score:100:age23

从上面的例子我们可以看出Students类没有实现Comparable接口，只是在sort()方法
中多传入一个参数，只不过该参数是一个接口我们需要实现其compare方法。

以上就是是Java中Colelctions工具类为我们提供的两种集合排序方法。

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