對List裡的物件元素進行排序
阿新 • • 發佈:2018-12-10
方法一:例項化一個比較器
public class Student { private int studentId; private String studentName; private int age; public Student(int studentId , String studentName, int age){ this.studentId=studentId; this.studentName=studentName; this.age=age; } public int getStudentId() { return studentId; } public void setStudentId(int studentId) { this.studentId = studentId; } public String getStudentName() { return studentName; } public void setStudentName(String studentName) { this.studentName = studentName; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }
import Java.util.ArrayList; import java.util.Collections; import java.util.Comparator; public class test { /** * @param args */ public static void main(String[] args) { Comparator<Student> comparator = new Comparator<Student>() { public int compare(Student s1, Student s2) { // 先排年齡 if (s1.getAge() != s2.getAge()) { return s1.getAge() - s2.getAge(); } else if (!s1.getStudentName().equals(s2.getStudentName())) { // 年齡相同則按姓名排序 return s1.getStudentName().compareTo(s2.getStudentName()); } else { // 姓名也相同則按學號排序 return s1.getStudentId() - s2.getStudentId(); } } }; Student stu1 = new Student (1,"zhangsan",28); Student stu2 = new Student (2,"zhagnsan",19); Student stu3 = new Student (3,"wangwu",19); Student stu4 = new Student (4,"wangwu",19); Student stu5 = new Student (5,"zhaoliu",18); ArrayList<Student> list = new ArrayList<Student>(); list.add(stu1); list.add(stu2); list.add(stu3); list.add(stu4); list.add(stu5); //這裡就會自動根據規則進行排序 Collections.sort(list,comparator); for(int i=0;i<list.size();i++){ Student stu=list.get(i); System.out.println("年齡:"+stu.getAge()+" 姓名:"+stu.getStudentName()+" 學號:"+stu.getStudentId()); } } }
方法二:實現Comparable介面
public class Student2 implements Comparable<Student2>{ private int studentId; private String studentName; private int age; public Student2(int studentId , String studentName, int age){ this.studentId=studentId; this.studentName=studentName; this.age=age; } public int getStudentId() { return studentId; } public void setStudentId(int studentId) { this.studentId = studentId; } public String getStudentName() { return studentName; } public void setStudentName(String studentName) { this.studentName = studentName; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public int compareTo(Student2 o) { if(age!=o.getAge()){ return age-o.getAge(); }else if(!studentName.equals(o.getStudentName())){ return studentName.compareTo(o.getStudentName()); }else { return studentId-o.getStudentId(); } } @Override public boolean equals(Object obj) { if(obj instanceof Student2){ Student2 stu=(Student2)obj; if((age==stu.getAge())&&(studentName.equals(stu.getStudentName()))&&(studentId==stu.getStudentId())){ return true; }else return true; }else{ return false; } } }
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class test2 {
/**
* @param args
*/
public static void main(String[] args) {
Student2 stu1 = new Student2 (1,"zhangsan",28);
Student2 stu2 = new Student2 (2,"zhagnsan",19);
Student2 stu3 = new Student2 (3,"wangwu",19);
Student2 stu4 = new Student2 (4,"wangwu",19);
Student2 stu5 = new Student2 (5,"zhaoliu",18);
ArrayList<Student2> list = new ArrayList<Student2>();
list.add(stu1);
list.add(stu2);
list.add(stu3);
list.add(stu4);
list.add(stu5);
//這裡就會自動根據規則進行排序
Collections.sort(list);
for(int i=0;i<list.size();i++){
Student2 stu=list.get(i);
System.out.println("年齡:"+stu.getAge()+" 姓名:"+stu.getStudentName()+" 學號:"+stu.getStudentId());
}
}
}
執行結果:
年齡:18 姓名:zhaoliu 學號:5
年齡:19 姓名:wangwu 學號:3
年齡:19 姓名:wangwu 學號:4
年齡:19 姓名:zhagnsan 學號:2
年齡:28 姓名:zhangsan 學號:1
注:大家可以看下api文件裡對介面 Comparable<T>介面的介紹,裡面說是建議重寫equals方法,否則可能出現怪異的表現