数值型数据(byte int short long float double)天生可对比大小,可排序,String实现了Comparable接口也可以对比大小与排序,而自定义类多种多样,没有一个共有的可以用作排序的指标,因此需要在自定义类中手动建立对比的方法,出于这个目的,java提供了两个接口Comparable与Comparator。
Collections.sort()底层排序依靠的是Arrays.sort(),而Arrays.sort()排序时采用的是冒泡法。
需要对比大小的对象可以实现Comparable接口,实现其中的抽象方法,该抽象方法用来设定比较的方式。下面以一个示例进行说明:
package com.javase.collections.comparable;public class Student implements Comparable<Student> {private String name;private int score;public Student() {super(); }public Student(String name, int score) {super();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; } @Overridepublic int compareTo(Student stu) {return this.score - stu.score;// 操作对象减去参数对象,升序排列,反之降序。 } }
在compareTo()方法中,以属性score为排序指标,采用“this.score-stu.score”,最终结果以升序排列,反之降序。
package com.javase.collections.comparable;import java.util.ArrayList;import java.util.Collections;import java.util.List;import org.junit.Test;public class ComparableTest { @Testpublic void testComparable() { List<Student> stus = new ArrayList<Student>(); Student zhangsan = new Student("zhangsan", 100); Student lisi = new Student("lisi", 90); Student wanger = new Student("wanger", 95); stus.add(zhangsan); stus.add(lisi); stus.add(wanger); System.out.println("排序前");for (Student x : stus) { System.out.println(x.getName() + "::" + x.getScore()); } System.out.println("排序后"); Collections.sort(stus);for (Student x : stus) { System.out.println(x.getName() + "::" + x.getScore()); } } }
输出:
如果一个类在创建时未实现Comparable接口,希望在不修改源码的情况下对其对象进行排序,可以在调用排序方法时实现Comparator比较器接口,指定排序方法。下面以一个示例进行说明:
package com.javase.collections.comparator;public class Student {private String name;private int score;public Student() {super(); }public Student(String name, int score) {super();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; } }
package com.javase.collections.comparator;import java.util.ArrayList;import java.util.Collections;import java.util.Comparator;import java.util.List;import org.junit.Test;public class ComparatorTest { @Testpublic void test() { List<Student> stus = new ArrayList<Student>(); Student zhangsan = new Student("zhangsan", 100); Student lisi = new Student("lisi", 90); Student wanger = new Student("wanger", 95); stus.add(zhangsan); stus.add(lisi); stus.add(wanger); System.out.println("排序前");for (Student x : stus) { System.out.println(x.getName() + "::" + x.getScore()); } System.out.println("-----------------------"); Collections.sort(stus, new Comparator<Student>() { @Overridepublic int compare(Student stu01, Student stu02) {// return stu01.getScore() - stu02.getScore();//升序return stu02.getScore() - stu01.getScore();// 降序 } }); System.out.println("排序后");for (Student x : stus) { System.out.println(x.getName() + "::" + x.getScore()); } } }
在compare(Student stu01, Student stu02)方法中,以属性score为排序指标,采用“stu01.score-stu02.score”,最终结果升序排列,反之降序。
输出:
以上是Comparable与Comparator的比较与使用的详细内容。更多信息请关注PHP中文网其他相关文章!