接口之Comparable

Posted 2020-11-23 liu-chen

本节讨论两个问题：

• 字符串数组的排序
• 自定义类的排序

1.实现字符串数组的排序

public class TestSort1 {

    public static void main(String[] args) {
        String[] strs=new String[] {"zhangsan","lisi","wangwu","zhaosi"};
        Arrays.sort(strs);
        System.out.print(Arrays.toString(strs));
    }
}

输出结果：按照首字母的字典顺序排序。
[lisi, wangwu, zhangsan, zhaosi

2.实现自定义类的排序

创建自定义类：

public class Employee1{
    private String name;
    private double salary;
    
    public Employee1(String name,Double salary) {
        this.name=name;
        this.salary=salary;
    }
    
    public String getName() {
        return name;
    }
    
    public double getSalary() {
        return salary;
    }
    
    public void raiseSalary(double byPercent){
        double raise=salary*byPercent/100;
        salary+=raise;
    }
    @Override
    public String toString() {
        return "Employee1 [name=" + name + ", salary=" + salary + "]";
    }
}

测试：

public class TestSort {

    public static void main(String[] args) {
        Employee1[] e1=new Employee1[3];
        e1[0]=new Employee1("zhangsan",5000.0);
        e1[1]=new Employee1("lisi",6000.0);
        e1[2]=new Employee1("wangwu",7500.0);
        Arrays.sort(e1);
        System.out.print(Arrays.toString(e1));

    }
}

 这样写完代码，编译器没有报错，但是一运行：

java.lang.ClassCastException

改进操作：

　　自定义的类要去implements Comparable接口，并定义接口中的方法

public class Employee1 implements Comparable<Employee1>{ //为泛型Comparable提供参数
    private String name;
    private double salary;
    
    public Employee1(String name,Double salary) {
        this.name=name;
        this.salary=salary;
    }
    
    public String getName() {
        return name;
    }
    
    public double getSalary() {
        return salary;
    }
    
    public void raiseSalary(double byPercent){
        double raise=salary*byPercent/100;
        salary+=raise;
    }

    @Override
    public String toString() {
        return "Employee1 [name=" + name + ", salary=" + salary + "]";
    }

    @Override
    public int compareTo(Employee1 o) {
        return Double.compare(o.salary,salary);
    }
}

 结果：

[Employee1 [name=wangwu, salary=7500.0], Employee1 [name=lisi, salary=6000.0], Employee1 [name=zhangsan, salary=5000.0]] 按照salary从高到低排布。

结论：要想使用Arrays.sort(),定义的类要去implements Comparable接口，实际上String类也都 implements Comparable接口。