集合排序案列

一：实体类准备

public class Student{
    private int id;
    private String name;
    private int age;
    public Student() {
        super();
        System.out.println("Student:执行了！");
    }
    public Student(int id, String name, int age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    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 int hashCode() {
        System.err.println("hashCode：方法执行了！");
        final int prime = 31;
        int result = 1;
        result = prime * result + age;
        result = prime * result + id;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }
    @Override
    public boolean equals(Object obj) {
        System.err.println("equals：方法执行了！");
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Student other = (Student) obj;
        if (age != other.age)
            return false;
        if (id != other.id)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age + "]";
    }
}

二：List-Map 按年龄升排

    @Test
    public void mapSort(){
        //LinkedHashMap<Integer, Student> map = new LinkedHashMap<>();
        //HashMap<Integer, Student> map = new HashMap<>();
        TreeMap<Integer, Student> map = new TreeMap<>();
        map.put(2, new Student(2,"ni",22));
        map.put(1, new Student(1,"wo",11));
        map.put(3, new Student(3,"ta",33));
        //将map转换出成list
        List<Entry<Integer, Student>> list =new ArrayList<>(map.entrySet());
        Collections.sort(list, new Comparator<Entry<Integer, Student>>() {
            @Override
            public int compare(Entry<Integer, Student> o1,Entry<Integer, Student> o2) {
                return o1.getValue().getAge()-(o2.getValue().getAge());//升序
            }
        });
        for (Entry<Integer, Student> entry : list) {
            System.out.println(entry.getValue());
        }
    }

三：set 按年龄降序

    @Test
    public void SetSort(){
        Set<Student> set=new HashSet<>();
        set.add(new Student(1,"wo",31));
        set.add(new Student(2,"ni",22));
        set.add(new Student(3,"ta",33));
        List<Student> list = Arrays.asList(set.toArray(new Student[set.size()]));
        Collections.sort(list,new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return o2.getAge()-o1.getAge();
            } 
        });
        for(Student s :list){
          System.out.println(s);
        }        
    }