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法律研究Java 中 compareTo() 和 compare() 方法的區別是什麼？\n
Comparable 介面提供了一個 compareTo() 方法用於物件的排序。此排序稱為類的自然排序，compareTo() 方法稱為其自然比較方法。Comparator 介面提供用於執行排序操作的方法。透過使用 Comparator 介面，我們可以執行多種排序序列。我們可以根據多個數據成員對物件進行排序。
compareTo()
compareTo() 方法將此物件與 o1 物件進行比較並返回一個整數。
語法
public int compareTo(Object o1)
- 當且僅當此物件小於 o1 時，它返回負數。
- 當且僅當此物件大於 o1 時，它返回正數。
- 當且僅當此物件等於 o1 時，它返回 0。
示例
import java.util.*;
class Employee implements Comparable {
String name;
int age;
Employee(String name, int age) {
this.name = name;
this.age = age;
}
//overridden compareTo method
@Override
public int compareTo(Object o) {
return this.age - ((Employee) o).age;
}
}
public class ComparableDemo {
public static void main(String[] args) {
// CREATION
List list = new ArrayList<>();
//INSERTION
list.add(new Employee("Krishna", 30));
list.add(new Employee("Archana", 28));
list.add(new Employee("Vineet", 25));
list.add(new Employee("Ramesh", 38));
list.add(new Employee("Alok", 28));
System.out.println("Before sorting: ");
for (Employee e : list) {
System.out.print("[ EMP : age = " + e.age + " ] ");
}
//SORTING
Collections.sort(list);
System.out.println("After sorting: ");
for (Employee e : list) {
System.out.print("[ EMP : age = " + e.age + " ] ");
}
}
}輸出
Before sorting: [ EMP : age = 2 ] [ EMP : age = 33 ] [ EMP : age = 11 ] [ EMP : age = 34 ] [ EMP : age = 7 ] After sorting: [ EMP : age = 2 ] [ EMP : age = 7 ] [ EMP : age = 11 ] [ EMP : age = 33 ] [ EMP : age = 34 ]
compare()
compare() 方法將第一個物件與第二個物件進行比較並返回一個整數
語法
public int compare (Object o1,Object o2)
- 當且僅當 o1 小於 o2 時，它返回負數
- 當且僅當 o1 大於 o2 時，它返回正數
- 當且僅當 o1 等於 o2 時，它返回 0
示例
import java.util.*;
class Student {
String name;
int age, roll;
Student(String name, int age, int roll) {
this.name = name;
this.age = age;
this.roll = roll;
}
}
class AgeComparator implements Comparator {
@Override
public int compare(Object o1, Object o2) {
return ((Student) o1).age - ((Student) o2).age;
}
}
class RollComparator implements Comparator {
@Override
public int compare(Object o1, Object o2) {
return ((Student) o1).roll - ((Student) o2).roll;
}
}
public class ComparatorDemo {
public static void main(String[] args) {
List list = new ArrayList<>();
list.add(new Student("Ramesh", 30, 20));
list.add(new Student("Adithya", 7, 10));
list.add(new Student("Krishna", 25, 5));
list.add(new Student("Vineet", 24, 15));
System.out.println("BEFORE SORTING");
for (Student e : list) {
System.out.println("[ STU : name = " + e.name + " age = " + e.age + " roll = " + e.roll + "]");
}
Collections.sort(list,new AgeComparator());
System.out.println("AFTER SORTING WITH AGE");
for (Student e : list) {
System.out.println("[ STU : name = " + e.name + " age = " + e.age + " ]");
}
Collections.sort(list,new RollComparator());
System.out.println("AFTER SORTING WITH ROLL");
for (Student e : list) {
System.out.println("[ STU : name = " + e.name + " roll = " + e.roll + " ]");
}
}
}輸出
BEFORE SORTING [ STU : name = Ramesh age = 30 roll = 20 ] [ STU : name = Adithya age = 7 roll = 10 ] [ STU : name = Krishna age = 25 roll = 5 ] [ STU : name = Vineet age = 24 roll = 15 ] AFTER SORTING WITH AGE [ STU : name = Adithya age = 7 ] [ STU : name = Vineet age = 24 ] [ STU : name = Krishna age = 25 ] [ STU : name = Ramesh age = 30 ] AFTER SORTING WITH ROLL [ STU : name = Krishna roll = 5 ] [ STU : name = Adithya roll = 10 ] [ STU : name = Vineet roll = 15 ] [ STU : name = Ramesh roll = 20 ]
更新於: 2020-02-06
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