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java之比较器

2024-09-10 20:09:06   206人阅读

java中的比较器有两种：

1、实体类实现Comparable接口，并实现其中的compareTo方法

2、在外部定义实现Comparator接口的比较器类，并实现其中的compare方法

Comparable接口

Person类源码：

package test;public class Person implements Comparable<Person> {    private Integer id;    private String name;    private Integer age;    public Person(Integer id, String name, Integer age) {        this.id = id;        this.name = name;        this.age = age;    }    @Override    public int compareTo(Person person) {        return name.compareTo(person.name);    }    public String toString() {        return id + "\t" + name + "\t" + age;    }    public int getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(Integer age) {        this.age = age;    }}

按名字进行排序，测试代码：

package test;import java.util.ArrayList;import java.util.Collections;import java.util.List;public class ComparableTest {    public static void main(String[] args) {        List<Person> list = new ArrayList<Person>();        list.add(new Person(1, "b", 13));        list.add(new Person(2, "d", 12));        list.add(new Person(3, "a", 12));        list.add(new Person(4, "a", 21));        Collections.sort(list);        System.out.println("编号\t姓名\t年龄");        for (Person p : list) {            System.out.println(p);        }    }}

打印：

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可以看出人员根据名字排序，当名字相等时，不做处理。

若要当名字相等时，年龄按从大到小排序，则修改Person类的compareTo方法，代码如下：

    public int compareTo(Person person) {        if (name.equals(person.name))            return -(age.compareTo(person.age));        return name.compareTo(person.name);    }

打印：

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Comparator接口

package test;public class Person  {    private Integer id;    private String name;    private Integer age;    public Person(Integer id, String name, Integer age) {        this.id = id;        this.name = name;        this.age = age;    }    public String toString() {        return id + "\t" + name + "\t" + age;    }    public int getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(Integer age) {        this.age = age;    }}

自定义比较器PersonComparator类，代码如下：

package test;import java.util.Comparator;public class PersonComparator implements Comparator<Person> {    public int compare(Person o1, Person o2) {        return o1.getName().compareTo(o2.getName());    }}

测试代码：

package test;import java.util.ArrayList;import java.util.Collections;import java.util.List;public class ComparatorTest {    public static void main(String[] args) {        List<Person> list = new ArrayList<Person>();        list.add(new Person(1, "b", 13));        list.add(new Person(2, "d", 12));        list.add(new Person(3, "a", 12));        list.add(new Person(4, "a", 21));        Collections.sort(list, new PersonComparator());        System.out.println("编号\t姓名\t年龄");        for (Person p : list) {            System.out.println(p);        }    }}

打印：

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java之比较器


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