下载：类与对象

Point.java

package cn.edu.bjut.chapter3;
 
class Point {
	private int x, y;
 
	public void setPoint(int a, int b) {
		x = a;
		y = b;
	}
 
	public int getX() {
		return x;
	}
 
	public int getY() {
		return y;
	}
 
	public String toString() {
		return "Point [x=" + x + ", y=" + y + "]";
	}
}

Rectangle.java

package cn.edu.bjut.chapter3;
 
public class Rectangle {
	double length = 0, width = 0; // 赋值语句
	// 初始化代码块
	{
		length = 1;
		width = 2;
	}
 
	// 构造函数
	public Rectangle(double len, double wid) {
		length = len;
		width = wid;
	}
 
	public double area() {
		return (length * width);
	}
 
	public static void main(String[] args) {
		Rectangle rect = new Rectangle(30, 20);
		System.out.println(rect.area());
	}
}

Rectangle.java

package cn.edu.bjut.chapter3;
 
public class Rectangle {
    double length, width; 
 
    // 构造函数
    public Rectangle(double length, double width) {
        this.length = length; 
        this.width = width;
    }
 
    // 构造函数
    public Rectangle(double length) {
        this(length, length)
    }
    ...
}

NoQualifier.java

package cn.edu.bjut.chapter3;
 
class NoQualifier {
	int a = 45; 
}

NoQualifierTester.java

package cn.edu.bjut.chapter3;
 
public class NoQualifierTester {
	public static void main(String[ ] args) { 
        NoQualifier nq = new NoQualifier( );
        System.out.println(nq.a);
    }
} 

Rectangle2.java

package cn.edu.bjut.chapter3;
 
public class Rectangle2 {
	double length, width;
 
	public Rectangle2(double length, double width) {
		this.length = length;
		this.width = width;
	}
 
	public double area() {
		return (length * width);
	}
}

PublicQualifierTester.java

package cn.edu.bjut.chapter3_1;
 
import cn.edu.bjut.chapter3.Rectangle2;
 
public class PublicQualifierTester {
	public static void main(String[] args) {
        Rectangle2 rect = new Rectangle2(30, 20); 
        System.out.println(rect.area());
 
        // 错误
        NoQualifier nq = new NoQualifier();
    }
}

Shape.java

package cn.edu.bjut.chapter3;
 
public abstract class Shape {
    abstract double area(); 
}

Rectangle3.java

package cn.edu.bjut.chapter3;
 
public class Rectangle3 extends Shape {
	double length, width;
 
	public Rectangle3(double length, double width) {
		this.length = length;
		this.width = width;
	}
 
	public double area() {
		return (length * width);
	}
}

Triangle.java

package cn.edu.bjut.chapter3;
 
public class Triangle extends Shape {
	double height, width;
 
	public Triangle(double height, double width) {
		this.height = height;
		this.width = width;
	}
 
	@Override
	double area() {
		return (height * width / 2);
	}
}

RectangleFinal.java

package cn.edu.bjut.chapter3;
 
public final class RectangleFinal {
    double length = 0, width = 0; // 赋值语句
 
    public Rectangle(double length, double width) {
        this.length = length; 
        this.width = width;
    }
 
 
    double area() {
        return (length*width);
    }
}

FinalTester.java

package cn.edu.bjut.chapter3;
 
// 错误
public class FinalTester extends RectangleFinal {
 
}

Student.java

package cn.edu.bjut.chapter3;
 
public class Student {
	private String name;
	private static String country = "中国";
 
	public Student(String name) {
		this.name = name;
	}
 
	public String toString() {
		return "name = " + name + ", country = " + country;
	}
 
	public static void main(String[] args) {
		Student s1 = new Student("何道昌");
		Student s2 = new Student("孙双双");
		System.out.println(s1 + "\n" + s2);
 
		s1.country = "日本";
		System.out.println(s1 + "\n" + s2);
 
		System.out.println(Student.country);
	}
}

Circle.java

package cn.edu.bjut.chapter3;
 
public class Circle {
	private double r;
	public static final double PI = 3.14;
 
	public Circle(double r) {
		this.r = r;
	}
 
	public double area() {
		return (r * r * PI);
	}
 
	public static void main(String[] args) {
		Circle c1 = new Circle(2);
		Circle c2 = new Circle(3);
		System.out.println(c1.area() + "\t" + c2.area());
	}
}

LocalVariableTester.java

package cn.edu.bjut.chapter3;
 
public class LocalVariableTester {
	static int add(int x, int y) {
		int z, d;
		z = x + y;
		// z = x + d;
		return z;
	}
 
	public static void main(String[] args) {
		int a = 2, b = 3;
		int f = add(a, b);
		System.out.println("f = " + f);
		// System.out.println("z = " + z);
		{
			int z = a + b;
			System.out.println("z = " + z);
		}
		// System.out.println("z = " + z);
	}
}

ParameterTester.java

package cn.edu.bjut.chapter3;
 
public class ParameterTester {
	static void add(double x, double y) {
		double z;
		z = x + y;
		System.out.println("z = " + z);
		x = x + 3.2;
		y = y + 1.2;
		System.out.println("x = " + x + "\ty = " + y);
	}
 
	static double add2(double y1, double y2) {
		double z;
		z = y1 + y2 + 2.9;
		return z;
	}
 
	public static void main(String[] args) {
		int a = 2, b = 7;
		double f1 = 2, f2 = 4, f3;
		add(a, b);// 按Java的类型转换规则达到形参类型
		System.out.println("a = " + a + "\tb = " + b);
		// f3 = add2(f1, f2, 3.5)；错，实参与形参参数个数不一致
		f3 = 2 + add2(f1, f2);
		System.out.println("f1 = " + f1 + "\tf2 = " + f2 + "\tf3 = " + f3);
	}
}

Factorial.java

package cn.edu.bjut.chapter3;
 
public class Factorial {
	static int calculate(int n) {
		if (n == 0) {
			return 1;
		} else {
			return (n * calculate(n - 1));
		}
	}
 
	public static void main(String[] args) {
		int n = 5;
		System.out.println(n + "! = " + calculate(n));
	}
}

• 定义一个Date类，兼顾大月、小月和闰年2月等日期的计算，须包括方法tomorrow()和daysInMonth()。
• 国际专利分类号（IPC）的前15位由section（部），class（大类），subclass（小类），main group（大组）和sub group（小组）五部分组成，每位的要求如下表所示，具体例子如：“G06F 17/30”和“H01M 10/587”，定义一个Ipc类，通过toString()函数将这五部分拼接成IPC的实际表现形式；

* 上题的Ipc类至少要包含两个构造函数，其中一个构造函数有五个参数（分别为部、大类、小类、大组和小组），另一个构造函数只有一个参数（以字符串形式表示的IPC分类号）。

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