假设Employee类包含一个int型成员id，一个 String型成员name，一个double型成员salar y。如果要求Employee可按id值比较大小，请编写Employee类。编写程序，创建几个Employee对象，将已们存放到TreeSet中并输出。

好的，以下是Employee类的实现代码：

import java.util.Objects;

public class Employee implements Comparable<Employee> {
    private int id;
    private String name;
    private double salary;

    public Employee(int id, String name, double salary) {
        this.id = id;
        this.name = name;
        this.salary = salary;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public double getSalary() {
        return salary;
    }

    @Override
    public int compareTo(Employee other) {
        return Integer.compare(this.id, other.id);
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", salary=" + salary +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Employee)) return false;
        Employee employee = (Employee) o;
        return id == employee.id &&
                Double.compare(employee.salary, salary) == 0 &&
                Objects.equals(name, employee.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name, salary);
    }
}

其中，我们实现了Comparable接口，重写了compareTo方法，以便能够按照id值比较大小。

接下来，我们可以编写测试代码，创建几个Employee对象，将它们存放到TreeSet中并输出：

import java.util.Set;
import java.util.TreeSet;

public class Main {
    public static void main(String[] args) {
        Employee emp1 = new Employee(3, "Alice", 5000.0);
        Employee emp2 = new Employee(1, "Bob", 6000.0);
        Employee emp3 = new Employee(2, "Charlie", 7000.0);

        Set<Employee> employees = new TreeSet<>();
        employees.add(emp1);
        employees.add(emp2);
        employees.add(emp3);

        for (Employee emp : employees) {
            System.out.println(emp);
        }
    }
}

输出结果应该是：

Employee{id=1, name='Bob', salary=6000.0}
Employee{id=2, name='Charlie', salary=7000.0}
Employee{id=3, name='Alice', salary=5000.0}