练习4：用Java实现某公司的人员分为员工和经理两种，但经理也属于员工中的一种，公司的人员都有自己的姓名和地址，员工和经理都有自己的工号、工资、工龄等属性，但经理不同于员工的是，经理有自己在公司对应的级别。假设每次给员工涨工资一次能涨10，经理能涨20%。本案例要求利用多态实现给员工和经理涨工资。

以下是实现该要求的Java代码：

class Employee {
    private String name;
    private String address;
    private int employeeId;
    private double salary;
    private int yearsOfService;

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

    public void increaseSalary() {
        salary += 10;
    }

    public String getName() {
        return name;
    }

    public String getAddress() {
        return address;
    }

    public int getEmployeeId() {
        return employeeId;
    }

    public double getSalary() {
        return salary;
    }

    public int getYearsOfService() {
        return yearsOfService;
    }
}

class Manager extends Employee {
    private int level;

    public Manager(String name, String address, int employeeId, double salary, int yearsOfService, int level) {
        super(name, address, employeeId, salary, yearsOfService);
        this.level = level;
    }

    public void increaseSalary() {
        salary *= 1.2;
    }

    public int getLevel() {
        return level;
    }
}

public class Company {
    public static void main(String[] args) {
        Employee employee1 = new Employee("John", "123 Main St.", 1001, 50000, 5);
        Manager manager1 = new Manager("Jane", "456 Oak St.", 1002, 80000, 10, 2);

        System.out.println("Before salary increase:");
        System.out.println(employee1.getName() + " earns " + employee1.getSalary() + " per year.");
        System.out.println(manager1.getName() + " earns " + manager1.getSalary() + " per year, and is at level " + manager1.getLevel() + " in the company.");

        employee1.increaseSalary();
        manager1.increaseSalary();

        System.out.println("After salary increase:");
        System.out.println(employee1.getName() + " earns " + employee1.getSalary() + " per year.");
        System.out.println(manager1.getName() + " earns " + manager1.getSalary() + " per year, and is at level " + manager1.getLevel() + " in the company.");
    }
}

在这段代码中，`Employee`类表示员工，`Manager`类表示经理，都继承自`Employee`类。`Employee`类有五个属性：姓名、地址、工号、工资和工龄，以及一个`increaseSalary()`方法，表示给员工涨工资。`Manager`类有一个额外的属性`level`，表示经理在公司中的级别，以及自己的`increaseSalary()`方法，表示给经理涨工资。

在主函数中，我们创建了一个`Employee`对象和一个`Manager`对象，然后分别调用它们的`increaseSalary()`方法来给它们涨工资。`Employee`对象的工资会增加10，而`Manager`对象的工资会增加20%。最后，我们输出员工和经理的新工资和经理的级别。