Java用CompareTo方法实现根据两个或多个属性对对象进行排序
2022/9/7 1:22:50
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CompareTo方法
CompareTo是String类的方法,CompareTo(Object o1,Object o2),就是用o1和o2进行比较
o1.compateTo(o2) 大于0 则o1大
o1.compateTo(o2) 小于0 则o2大
o1.compateTo(o2) 等于0 则一样大
升序降序
升序:
public static void main(String[] args) { ArrayList<String> list = new ArrayList<>(); list.add("111"); list.add("222"); list.add("333"); Collections.sort(list, new Comparator<String>() { @Override public int compare(String o1, String o2) { if(o1.compareTo(o2)>0){ return 1; } return -1; } }); System.out.println(list); }
结果:
[111, 222, 333]
降序:
public static void main(String[] args) { ArrayList<String> list = new ArrayList<>(); list.add("111"); list.add("222"); list.add("333"); Collections.sort(list, new Comparator<String>() { @Override public int compare(String o1, String o2) { if(o1.compareTo(o2)<0){ return 1; } return -1; } }); System.out.println(list); }
结果:
[333, 222, 111]
根据对象两个属性排序实现方法
Student对象三个属性:id、username、age,要求:要根据username升序、age降序的方法对student进行排序。
Student stu1 = new Student(1, "333", "333"); Student stu2 = new Student(2, "111", "111"); Student stu3 = new Student(3, "333", "222"); Student stu4 = new Student(4, "222", "111"); Student stu5 = new Student(5, "333", "111");
需求:
代码实现:
Student:
public class Student { private int id; private String username; private String age; public Student(int id, String username, String age) { this.id = id; this.username = username; this.age = age; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getAge() { return age; } public void setAge(String age) { this.age = age; } @Override public String toString() { return "Student{" + "id=" + id + ", username='" + username + '\'' + ", age='" + age + '\'' + '}'; } }
实现代码:
public static void main(String[] args) { ArrayList<Student> list = new ArrayList<>(6); Student stu1 = new Student(1, "333", "333"); Student stu2 = new Student(2, "111", "111"); Student stu3 = new Student(3, "333", "222"); Student stu4 = new Student(4, "222", "111"); Student stu5 = new Student(5, "333", "111"); list.add(stu1); list.add(stu2); list.add(stu3); list.add(stu4); list.add(stu5); Collections.sort(list, new Comparator<Student>() { @Override public int compare(Student o1, Student o2) { if(o1.getUsername().compareTo(o2.getUsername())>0){ return 1; }else if(o1.getUsername().compareTo(o2.getUsername())==0){ if(o1.getAge().compareTo(o2.getAge())<0){ return 1; } } return -1; } }); for (Student stu:list) { System.out.println(stu); } }
结果:
Student{id=1, username='111', age='111'} Student{id=2, username='222', age='111'} Student{id=3, username='333', age='333'} Student{id=4, username='333', age='222'} Student{id=5, username='333', age='111'}
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