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接下来是以下内容的优化版本：

一、数字处理

给一个不多于5位的正整数。

（1）求它是几位数

将输入的数字转换为字符串，计算其长度即可确定位数。

（2）逆序打印出各位数字

将字符串转换为字符数组，从末尾开始遍历，依次输出字符即可得到逆序结果。

二、数组操作

编写一个类并验证它是否有效，该类包含一个维数组成员变量，完成数组的赋值与输出。

class test {
    int[] nums = new int[5];
}

使用示例

test t = new test();
for (int i = 0; i < t.nums.length; i++) {
    t.nums[i] = i;
}
for (int i = 0; i < t.nums.length; i++) {
    System.out.println(t.nums[i]);
}

三、工资查询系统

实现一个工资查询的程序，支持三类员工：项目经理、 高级程序员、 程序员。

基于工资计算的规则

实现代码

interface Factory {
    int searchSalary(String position);
    int workTime(int day, String position);
}
class Manager implements Factory {
    @Override
    public int searchSalary(String position) {
        int salary = 15000;
        System.out.println(position + "正常的工资为: " + salary);
        return salary;
    }
    @Override
    public int workTime(int day, String position) {
        int salary = 15000;
        int final_salary = salary + 800 * day;
        System.out.println(position + "加班后的工资为: " + final_salary);
        return final_salary;
    }
}
class SeniorProgrammer implements Factory {
    @Override
    public int searchSalary(String position) {
        int salary = 10000;
        System.out.println(position + "正常的工资为: " + salary);
        return salary;
    }
    @Override
    public int workTime(int day, String position) {
        int salary = 10000;
        int final_salary = salary + 500 * day;
        System.out.println(position + "加班后的工资为: " + final_salary);
        return final_salary;
    }
}
class Programmer implements Factory {
    @Override
    public int searchSalary(String position) {
        int salary = 5000;
        System.out.println(position + "正常的工资为: " + salary);
        return salary;
    }
    @Override
    public int workTime(int day, String position) {
        int salary = 5000;
        int final_salary = salary + 200 * day;
        System.out.println(position + "加班后的工资为: " + final_salary);
        return final_salary;
    }
}
class FactoryImpl {
    public void useBegin(Factory fac, String position) {
        fac.searchSalary(position);
    }
    public void useFinal(Factory fac, int day, String position) {
        fac.workTime(day, position);
    }
}
public class Main {
    public static void main(String[] args) {
        FactoryImpl f = new FactoryImpl();
        f.useBegin(new Manager(), "项目经理");
        f.useFinal(new Manager(), 6, "项目经理");
        f.useBegin(new SeniorProgrammer(), "高级程序员");
        f.useFinal(new SeniorProgrammer(), 7, "高级程序员");
        f.useBegin(new Programmer(), "程序员");
        f.useFinal(new Programmer(), 8, "程序员");
    }
}

四、计算器功能

利用接口做参数，编写一个计算器，支持加减乘除运算。

接口定义

interface Computer {
    int computer(int n, int m);
}

实现类

class Add implements Computer {
    @Override
    public int computer(int n, int m) {
        int value = n + m;
        System.out.println("n + m = " + value);
        return value;
    }
}
class Sub implements Computer {
    @Override
    public int computer(int n, int m) {
        int value = n - m;
        System.out.println("n - m = " + value);
        return value;
    }
}
class Multiply implements Computer {
    @Override
    public int computer(int n, int m) {
        int value = n * m;
        System.out.println("n * m = " + value);
        return value;
    }
}
class Divide implements Computer {
    @Override
    public int computer(int n, int m) {
        if (m != 0) {
            int value = n / m;
            System.out.println("n / m = " + value);
            return value;
        } else {
            System.out.println("分母不能为零");
            return 0;
        }
    }
}
class UseCompute {
    public UseCompute(int n, int m) {
        System.out.println("n的值为:" + n + ", m的值为:" + m);
    }
    public void useCom(Computer com, int n, int m) {
        com.computer(n, m);
    }
}
public class Main {
    public static void main(String[] args) {
        UseCompute uc = new UseCompute(20, 10);
        uc.useCom(new Add(), 20, 10);
        uc.useCom(new Sub(), 20, 10);
        uc.useCom(new Multiply(), 20, 10);
        uc.useCom(new Divide(), 20, 10);
    }
}

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