Java对象的比较

目录

实现Comparable接口,重写compareTo方法

创建比较器,实现Comparator接口,重写compare方法

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创建一个学生类

class Student {
    public String name;
    public int age;

    public Student(String name,int age){
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    
}

执行以下代码

public class Test {
    public static void main(String[] args) {
        Student[] students = new Student[3];
        students[0] = new Student("bit",10);
        students[1] = new Student("hello",11);
        students[2] = new Student("abc",12);
        Arrays.sort(students);
        System.out.println(Arrays.toString(students));
    }
}

会出现类型转换异常

这是因为我们在进行数组排序的时候,由于我们数组元素的类型是自定义的student类,但是我们没有规定student比较的规则,所以会报错.

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实现Comparable接口,重写compareTo方法

在这里,我们可以根据学生的年龄进行排序

class Student implements Comparable{
    public String name;
    public int age;

    public Student(String name,int age){
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }


    @Override
    public int compareTo(Student o) {
        return this.age-o.age;
    }
}

重写方法后,我们就可以调用此方法来进行学生之间的比较

public static void main(String[] args) {
        Student student1 = new Student("zhangsan",15);
        Student student2 = new Student("lisi",16);
        if (student1.compareTo(student2) > 0){
            System.out.println("zhangsan 比 lisi 大!");
        }else if (student1.compareTo(student2) == 0){
            System.out.println("zhsangsan 和 lisi 一样大!");
        }else {
            System.out.println("zhangsan 比 lisi 小!");
        }
    }

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创建比较器,实现Comparator接口,重写compare方法

上述比较的方法,对类的侵入性比较强,不够灵活,如果改变比较规则,则 需要改动原先的代码.

比较器相对于上述方法能够更加灵活.

如果我们要根据年龄进行比较,就实现一个年龄的比较器.

class AgeComparator implements Comparator{

    @Override
    public int compare(Student o1, Student o2) {
        return o1.age-o2.age;
    }
}

如果要根据名字进行比较,就实现一个名字的比较器.

class NameComparator implements Comparator{

    @Override
    public int compare(Student o1, Student o2) {
        return o1.name.compareTo(o2.name);
    }
}

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 public static void main(String[] args) {
        Student[] students = new Student[3];
        students[0] = new Student("bit",10);
        students[1] = new Student("hello",11);
        students[2] = new Student("abc",12);
        AgeComparator ageComparator = new AgeComparator();
        NameComparator nameComparator = new NameComparator();
        Arrays.sort(students,nameComparator);
        System.out.println(Arrays.toString(students));
    }

这样,我们就可以在Arrays.sort方法中传入比较器,根据我们自己制定的比较规则进行比较.

也可以直接调用比较器中的方法进行比较.

public static void main(String[] args) {
        Student student1 = new Student("zhangsan",15);
        Student student2 = new Student("lisi",16);
        AgeComparator ageComparator = new AgeComparator();
        int l = ageComparator.compare(student1,student2);
        if (l > 0){
            System.out.println("s1 > s2");
        }else {
            System.out.println("s1 < s2");
        }
    }

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