Chapter 07 OOP初级 part3

本章练习

以下代码均已编译通过

public class Homework01 {
    public static void main(String[] args) {
        double[] arr = {2.45, 45.4, -4324.4, 434.7, 2.76};
        A01 m =  new A01();
        Double ret = m.max(arr);
        if(ret != null){
            System.out.println("最大值为："+ret);
        }else{
            System.out.println("Wrong input!");
        }

    }
}
//完成基本功能后，再考虑健壮性
class A01{
    // 包装类 Double
    public Double max(double[] arr){
        // 先判不为空，再判长度大于零
        if(arr != null && arr.length > 0){

            double max = arr[0];    // 假定第一个数就是最大
            for (int i = 1; i < arr.length; i++) {
                if(arr[i] > max){
                    max = arr[i];
                }
            }
            return max;
        }else{
            return null;
        }
    }
}

public class Homework02 {
    public static void main(String[] args) {
        A02 p = new A02();
        String[] arr = {"Tim", "Jack", "Mary"};
        System.out.println(p.find(arr, "Jack"));
        System.out.println(p.find(arr, "Java"));
    }
}

class A02 {
    public int find(String[] arr, String partten){
        if(arr != null && arr.length > 0){
            for(int i = 0; i < arr.length; i++){
                if(partten.equals(arr[i])){
                    return i;
                }
            }
        }
        return -1;
    }
}

public class Homework03 {
    public static void main(String[] args) {
        Book b1 = new Book("三体", 120.99);
        b1.info();
        b1.updatePrice();
        b1.info();
    }
}

class Book {
    String name;
    double price;
    public Book(String name, double price){
        this.name = name;
        this.price = price;
    }
    public void updatePrice(){
        if(this.price > 150){
            this.price = 150;
        }else if(this.price > 100){
            this.price = 100;
        }
    }

    public void info(){
        System.out.println(this.name + "的价格为：" + this.price);
    }
}

public class Homework04 {
    public static void main(String[] args) {
        int[] arr = {1, 4, 6, 2, 3};
        A03 a = new A03();
        int[] newArr = a.copyArr(arr);
        for (int i = 0; i < newArr.length; i++) {
            System.out.print(newArr[i] + "\t");
        }
    }
}

class A03 {
    public int[] copyArr(int[] oldArr){
        // 在堆中创建一个长度为 oldArr.length 的数组
        int[] newArr = new int[oldArr.length];
        for(int i = 0; i < oldArr.length; i++){
            newArr[i] = oldArr[i];
        }
        return newArr;
    }
}

public class Homework05 {
    public static void main(String[] args) {
        Circle circle = new Circle(3);
        System.out.printf("周长为：%.2f\n", circle.perimeter());
        System.out.printf("面积为：%.2f", circle.area());
    }
}

class Circle {
    double radius;

    public Circle(double radius){
        this.radius = radius;
    }
    // 周长
    public double perimeter(){
        return 2.0 * this.radius * Math.PI;
    }
    // 面积
    public double area(){
        return Math.PI * this.radius * this.radius;
    }
}

public class Homework06 {
    public static void main(String[] args) {
        Cale cale = new Cale(20, 4);
        System.out.println(cale.add());
        System.out.println(cale.sub());
        System.out.println(cale.mul());
        if(cale.div() != null){
            System.out.println(cale.div());
        }
        Cale cale1 = new Cale(20, 0);
        if(cale1.div() != null){
            System.out.println(cale1.div());
        }
    }
}

class Cale {
    double op1, op2;

    public Cale(double op1, double op2){
        this.op1 = op1;
        this.op2 = op2;
    }

    double add(){
        return op1 + op2;
    }

    double sub(){
        return op1 - op2;
    }

    double mul(){
        return op1 * op2;
    }

    Double div(){
        if(op2 == 0){
            System.out.println("除数不能为零"); 
            return null;    
        }else{
            return op1 / op2;
        }
    }
}

public class Homework07 {
    public static void main(String[] args) {
        Dog dog = new Dog("大黄", "White", 4);
        dog.show();
    }
}

class Dog {
    String name;
    String color;
    int age;

    public Dog(String name, String color, int age){
        this.name = name;
        this.color = color;
        this.age = age;
    }

    public void show(){
        System.out.println("名字=" + this.name + 
                            " 颜色=" + this.color+
                            " 年龄=" + this.age);
    }
}

public class Homework07 {
    public static void main(String[] args) {
        Dog dog = new Dog("大黄", "White", 4);
        dog.show();
    }
}

class Dog {
    String name;
    String color;
    int age;

    public Dog(String name, String color, int age){
        this.name = name;
        this.color = color;
        this.age = age;
    }

    public void show(){
        System.out.println("名字=" + this.name + 
                            " 颜色=" + this.color+
                            " 年龄=" + this.age);
    }
}

9.略

10.输出为：

i=101

j=100

101

101

public double method(double n1, double n2){...}

public class Homework12 {
    public static void main(String[] args) {
        Emploee emploee = new Emploee("Tim", "male", 20);
        System.out.println(emploee.name + "\t" + 
                        emploee.gender + "\t" + emploee.age);
    }
}

class Emploee {
    String name;
    String gender;
    int age;
    String position;
    int salary;

    public Emploee(String position, int salary){
        this.position = position;
        this.salary = salary;
    }

    public Emploee(String name, String gender, int age){
        this.name = name;
        this.gender = gender;
        this.age = age;
    }

    public Emploee(String name, String gender, int age, String position, int salary) {
        this(name, gender, age);    // 复用第二个构造器，注意不能同时复用前两个
        this.position = position;
        this.salary = salary;
    }
}

public class Homework13 {
    public static void main(String[] args) {
        new PassObject().printAreas(5);
    }
}

class Circle {
    double radius;

    public Circle(double radius){
        this.radius = radius;
    }
    
    public double findArea(){
        return radius * radius * Math.PI;
    }
}

class PassObject {
    public void printAreas(int times){
        System.out.println("Radius" + "\t" + "Area");
        for(double i = 1.0; i <= times; i++){
            System.out.print(i + "\t");
            System.out.print(new Circle(i).findArea());
            System.out.println();
        }
    }
}

import java.util.Random;
import java.util.Scanner;

import javax.lang.model.util.ElementScanner6;

public class Homework14 {
    public static void main(String[] args) {
        // 创建扫描器接收数据
        Scanner scanner = new Scanner(System.in);
        Tom tom = new Tom();
        System.out.println("输入你想玩的局数:");
        int countTotal = scanner.nextInt();
        // 循环 countToatal 次
        for(int i = 1; i <= countTotal; i++){
            System.out.println("请出拳: 0-拳头  1-石头  2-剪刀 ");
            tom.tomGuessNum = scanner.nextInt();
            tom.setTomGuessNum(tom.tomGuessNum);
            tom.comGuessNum = tom.computerNum();
            String outcome = tom.vsComputer();
            tom.winCountNum = tom.winCount(outcome);
            tom.showInfo(i, outcome);
        }
        System.out.println("你总共赢了：" + tom.winCountNum + "局");
        scanner.close();
    }
}

class Tom{
    int tomGuessNum;
    int comGuessNum;
    int winCountNum;
    // 显示当前局信息
    public void showInfo(int count, String outcome){
        System.out.println("==================================================================");
        System.out.println("当前局数\t你的出拳\t电脑出拳\t结果");
        System.out.println(count + "\t\t" + tomGuessNum  + "\t\t" 
                        + comGuessNum + "\t\t" + outcome);
        System.out.println("==================================================================");
    }

    public int computerNum(){
        Random r = new Random();
        return r.nextInt(3);    // 0-2的随机数
    }

    public void setTomGuessNum(int tomGuessNum){
        if(tomGuessNum > 2 || tomGuessNum < 0){
            throw new IllegalArgumentException("输入有误");
        }
        this.tomGuessNum = tomGuessNum;
    }

    public int getTomGuessNum(){
        return tomGuessNum;
    }

    public String vsComputer(){
        if(tomGuessNum == 0 && comGuessNum ==1 
        || tomGuessNum ==1 && comGuessNum == 2
        || tomGuessNum == 2 && comGuessNum == 0){
            return "你赢了";
        }else if(tomGuessNum == comGuessNum){
            return "平局";
        }else{
            return "你输了";
        }
    }

    public int winCount(String s){
        if(s.equals("你赢了")){
            winCountNum++;
        }
        return winCountNum;
    }

}