Java基础 4.21

1.本章类知识相关练习

public class Homework02 {
	public static void main(String[] args) {
		A03 a03 = new A03();
		int[] arr = {1, 123, 345, 456};
		int[] arr2 = a03.copyArr(arr);
		for (int i = 0; i < arr2.length; i++) {
			System.out.print(arr2[i] + " ");
		}
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i] + " ");
		}
		System.out.println();
		System.out.println(arr2.hashCode());
		System.out.println(arr.hashCode());
		Circle circle = new Circle(5);
		circle.areaMth();
		circle.perimeterMth();
		Cale cale = new Cale(5.7, 0);
		cale.sum();
		cale.sub();
		cale.mul();
		Double res = cale.division();
		if (res != null) {
			System.out.println(res);
		}
		

	}
}
//编写类A03 实现数组的复制功能copyArr，输入旧数组，返回一个新数组
//元素和旧数组一样
class A03 {
	public int[] copyArr(int[] arr) {
		int[] newArr = new int[arr.length];
		for (int i = 0; i < arr.length; i++) {
			newArr[i] = arr[i];
		}
		return newArr;
	}
}

//定义一个圆类Circle，定义属性: 半径 提供显示圆周长功能的方法
//提供显示圆面积的方法
class Circle {
	double radius;
	public Circle(double radius) {
		this.radius = radius;
	}
//若要返回值也可改为double 为了显示方便所以不返回值 用void
	public void perimeterMth() {
		double perimeter = 2 * Math.PI * radius;
		System.out.println("perimeter = " + perimeter);
	}

	public void areaMth() {
		double area = Math.PI * radius * radius;
		System.out.println("area = " + area);
	}
}

//编程创建一个Cale计算类 在其中定义2个变量表示两个操作数 定义四个方法
//实现求和 差 乘 商(要求除数为0的话 要提示) 并创建两个对象 分别测试
class Cale {
	double num1;
	double num2;
	public Cale(double num1, double num2) {
		this.num1 = num1;
		this.num2 = num2;
	}

	public double sum() {
		System.out.println(num1 + num2);
		return num1 + num2;
	}

	public double sub() {
		System.out.println(num1 - num2);
		return num1 - num2;
	}

	public double mul() {
		System.out.println(num1 * num2);
		return num1 * num2;
	}

	public Double division() {
		//用一个方法将其置为空
		if (num2 == 0) {
			System.out.println("被除数不能为0");
			return null;
		} else {
			System.out.println(num1 / num2);
			return num1 / num2;
		}

	}
}

//设计一个Dog类，有名字、颜色和年龄属性，定义输出方法show()
//显示其信息 并创建对象 进行测试
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("name = " + name + " color = " + color + " age = " + age);
	}
}

public class Homework01_2 {
	int count = 9;
	public void count1() {
		count = 10;
		System.out.println("count1 = " + count);
	}

	public void count2() {
		System.out.println("count1 = " + count++);
	}
	//任何一个类都可有main
	public static void main(String[] args) {
		//new Homework01_2() 是匿名对象 匿名对象使用后就不能使用
		//new Homework01_2() count1()创建好匿名对象后，就调用count1()
		new Homework01_2().count1();
		Homework01_2 t1 = new Homework01_2();
		t1.count2();
		t1.count2();
	}

}

// 代码理解题
public class Homework01_2 {
	int count = 9;
	public void count1() {
		count = 10;
		System.out.println("count1 = " + count);
	}

	public void count2() {
		System.out.println("count1 = " + count++);
	}
//任何一个类都可有main
	public static void main(String[] args) {
		// new Homework01_2() 是匿名对象 匿名对象使用后就不能使用
		// new Homework01_2() count1()创建好匿名对象后，就调用count1()
		new Homework01_2().count1();
		Homework01_2 t1 = new Homework01_2();
		t1.count2();
		t1.count2();
		Music music = new Music("logic", 180);
		music.play();
		System.out.println(music.getInfo());

	}
}

// 定义Music类 里面有音乐名name 音乐时长times属性
// 并有播放器play功能和返回本身属性信息的功能方法getInfo
class Music {
	String name;
	double times;
	public Music(String name, double times) {
		this.name = name;
		this.times = times;
	}

	public void play() {
		System.out.println("the music is playing!");
	}

	public String getInfo() {
		return name + " " +times;
	}


}

//创建一个Employee类 属性有(名字 性别 年龄 职位 薪水)
//提供3个构造器 可以初始化(名字 性别 年龄 职位 薪水)
//(名字 性别 年龄) (职位 薪水) 要求充分复用构造器
public class Homework01_3 {
	public static void main(String[] args) {
		
	}
}

class Employee {
	String name;
	char gender;
	int age;
	String label;
	double salary;

	public Employee(String label, double salary) {
		this.label = label;
		this.salary = salary;
	}

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

	public Employee(String name, char gender, int age, String label,
					double salary) {
		this(name, gender, age);//使用前面的构造器
		this.label = label;
		this.salary = salary;

	}
}

//将对象作为参数传递给方法。
//题目要求:(1)定义一个Circle类，包含一个double型的radius属性代表圆的半径，findArea()方法返回圆的面积。
//(2)定义一个类PassObject，在类中定义一个方法printAreas()，该方法的定义如下:public void printAreas(Circle c, int times) 方法签名
//(3)在printAreas方法中打印输出1到times之间的每个整数半径值，以及对应的面积。例如，times为5，则输出半径1，2，3，4，5，以及对应的圆面积
//(4)在main方法中调用printAreas()方法，调用完毕后输出当前半径值。程序运行结果如图所示
public class Homework01_4 {
	public static void main(String[] args) {
		Circle c = new Circle();
		PassObject pass = new PassObject();
		pass.printAreas(c, 5);
	}
}

class Circle {
	double radius;
	// public Circle(double radius) {
	// 	this.radius = radius;
	// }
	public double findArea() {//返回面积
		return Math.PI * radius * radius;
	}
	//添加方法setRadius 修改对象的额半径值
	public void setRadius(double radius) {
		this.radius = radius;
	}
}

class PassObject {
	public void printAreas(Circle c, int times) {
		System.out.println("Radius\tAreas");
		for (int i = 1; i <= times; i++) {//输出1到times之间的每个整数半径值
			c.setRadius(i);//修改c对象半径值
			System.out.println((double)i + "\t" + c.findArea());
		}
	}
}