compareTo(Object obj)
方法,两个对象即通过 compareTo(Object obj) 方法的返回值来比较大小。如果当前对象this大于形参对象obj,则返回正整数,如果当前对象this小于形参对象obj,则返回负整数,如果当前对象this等于形参对象obj,则返回零。package java.lang;
public interface Comparable{
int compareTo(Object obj);
}
示例代码:
public class Student implements Comparable {
private String name;
private int score;
public Student(String name, int score) {
this.name = name;
this.score = score;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", score=" + score +
'}';
}
@Override
public int compareTo(Object o) {
return this.score - ((Student)o).score;
}
}
@Test
public void test02() {
Student[] students = new Student[3];
students[0] = new Student("张三", 96);
students[1] = new Student("李四", 85);
students[2] = new Student("王五", 98);
System.out.println(Arrays.toString(students));
Arrays.sort(students);
System.out.println(Arrays.toString(students));
}
使用背景: 当元素没有实现java.lang.Comparable
接口而又不方便改代码,或者是实现了Comparable
接口,也指定了两个对象的比较大小的规则,但此时不想按照预定义的方法比较大小。
所以又增加了一个java.util.Comparator接口。强行对多个对象进行整体排序的比较。
compare(Object o1,Object o2)
方法,比较o1和o2的大小:如果方法返回正整数,则表示o1大于o2;如果返回0,表示相等;返回负整数,表示o1小于o2。Comparator
传递给 sort
方法(如 Collections.sort
或 Arrays.sort
),从而允许在排序顺序上实现精确控制。package java.util;
public interface Comparator{
int compare(Object o1,Object o2);
}
示例:
import java.util.Comparator;
//定义定制比较器类
public class StudentScoreComparator implements Comparator {
@Override
public int compare(Object o1, Object o2) {
Student s1 = (Student) o1;
Student s2 = (Student) o2;
int result = s1.getScore() - s2.getScore();
return result != 0 ? result : s1.getId() - s2.getId();
}
}
@Test
public void test01() {
Student[] students = new Student[5];
students[0] = new Student(3, "张三", 90, 23);
students[1] = new Student(1, "熊大", 100, 22);
students[2] = new Student(5, "王五", 75, 25);
students[3] = new Student(4, "李四", 85, 24);
students[4] = new Student(2, "熊二", 85, 18);
System.out.println(Arrays.toString(students));
//定制排序
StudentScoreComparator sc = new StudentScoreComparator();
Arrays.sort(students, sc);
System.out.println("排序之后:");
System.out.println(Arrays.toString(students));
}
Goods[] all = new Goods[4];
all[0] = new Goods("War and Peace", 100);
all[1] = new Goods("Childhood", 80);
all[2] = new Goods("Scarlet and Black", 140);
all[3] = new Goods("Notre Dame de Paris", 120);
Arrays.sort(all, new Comparator() {
@Override
public int compare(Object o1, Object o2) {
Goods g1 = (Goods) o1;
Goods g2 = (Goods) o2;
return g1.getName().compareTo(g2.getName());
}
});
System.out.println(Arrays.toString(all));