Java：抽象类和接口（3）-优快云博客

一大小比较

1.comparable

问题：1.当前的自定义类，要根据什么规则进行大小的比较？

2.这个规则怎么定义？

public class Student implements Comparable<Student>{

public Student(String name, int age){
        this.name=name;
        this.age=age;

    }
    public String name;
    public int age;

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
    public static void main1(String[] args) {
        Student student1=new Student("zhangsan",12);
        Student student2=new Student("lisi",8);
        System.out.println(student1 > student2);

    }
}

无法进行比较，因为无法区分是年龄还是姓名的比较，比较的是地址，那么我们就要借用 comparable来进行比较

public class Student implements Comparable<Student>{
 public Student(String name, int age){
        this.name=name;
        this.age=age;

    }
    public String name;
    public int age;

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

    @Override
    public int compareTo(Student o) {
       /* if(this.age>o.age){
            return 1;
        }else if(this.age==o.age){
            return 0;
        }else {
            return -1;
        }*/
        //return  this.age - o.age;
        return this.name.compareTo(o.name);
    }
}  


public static void main(String[] args) {
        Student student1=new Student("zhangsan",12);
        Student student2=new Student("lisi",8);
        System.out.println(student1.compareTo(student2));
    }

通过学生这个类来实现 comparable这个接口，然后再重写comparable这个接口里面的compareTo方法，进行比较。

看一下comparable的源代码

1.1年龄的比较

    public int compareTo(Student o) {
       /* if(this.age>o.age){
            return 1;
        }else if(this.age==o.age){
            return 0;
        }else {
            return -1;
        }*/
        return  this.age - o.age;
    }
}

1.2姓名的比较

    public int compareTo(Student o) {
        return this.name.compareTo(o.name);
    }
}

让我们来自己实现一个排序，了解一下排序是怎么做的。

    public static void mySort(Comparable[] comparable){
        for (int i = 0; i<comparable.length-1; i++) {
            for (int j = 0; j < comparable.length - 1 - i; j++) {
                if(comparable[j].compareTo(comparable[j+1])>0) {
                    Comparable tem = comparable[j];
                    comparable[j] = comparable[j + 1];
                    comparable[j + 1] = tem;
                }
            }
        }
    }

2.Comparator

但是使用comparable只能进行单一的比较，所以我们可以使用Comparator，定义两个类AgeComparator和NameComparator分别实现Comparator接口

看一下Comparator接口的源代码

public class AgeComparator implements Comparator<Student> {

    @Override
    public int compare(Student o1, Student o2) {
        return o1.age-o2.age;
    }
}
public class NameComparator implements Comparator<Student> {

    @Override
    public int compare(Student o1, Student o2) {
        return o1.name.compareTo(o2.name);
    }
}
    public static void main4(String[] args) {
        Student[] students=new Student[3];
        students[0]=new Student("zhangsan",12);
        students[1]=new Student("afs",19);
        students[2]=new Student("lisi",8);
        System.out.println("排序前"+ Arrays.toString(students));

        AgeComparator ageComparator=new AgeComparator();
        Arrays.sort(students,ageComparator);
        System.out.println("年龄排序后"+Arrays.toString(students));
        NameComparator nameComparator=new NameComparator();
        Arrays.sort(students,nameComparator);
        System.out.println("姓名排序后"+Arrays.toString(students));


    }

由于Java语法非常灵活，我们也可以用这种方法来接受

    public static void main3(String[] args) {
        Student student1=new Student("zhangsan",12);
        Student student2=new Student("lisi",8);
        AgeComparator ageComparator=new AgeComparator();
        int ret=ageComparator.compare(student1,student2);
        System.out.println(ret);
    }

二两个数值的交换

在之前的学习中，如果我们要把两个数的值交换，我们会这样做

public class Test {
    public static void chat(int x,int y){
        int tem=x;
        x=y;
        y=tem;
    }
    public static void main(String[] args) {
        int a=10;
        int b=20;
        chat(a,b);
        System.out.println(a+"  "+b);
    }
}

但是我们可以发现他们的值没有任何变化

我们可以通过图像来观察

但是我们可以用封装的方法

class MyNum{
    public int num;
}
public class Test {
    public static void chatNum(MyNum myNum1,MyNum myNum2){
        int tem=myNum1.num;
        myNum1.num=myNum2.num;
        myNum2.num=tem;
    }

    public static void main(String[] args) {
        MyNum myNum1=new MyNum();
        MyNum myNum2=new MyNum();
        myNum1.num=10;
        myNum2.num=200;
        System.out.println(myNum1.num);
        System.out.println(myNum2.num);
        System.out.println("------");
        chatNum(myNum1,myNum2);
        System.out.println(myNum1.num);
        System.out.println(myNum2.num);

    }

过程如图所示