浙大《面向对象程序设计--java语言》学习笔记（第一周：类与对象）

1.1用类制造对象

 

 

 1.2定义类

这里我们定义了一个类

这里我们写一个VendingMachine的类

package vendingmachine;

public class VendingMachine {
	int price = 80;
	int balance;
	int total;
	
	void showPrompt()
	{
		System.out.println("Welcome");
	}
	
	void insertMoney(int amount) {
		balance = balance + amount;
	}
	
	void showBalance() {
		System.out.println(balance);
	}
	
	void getFood() {
		if(balance >= price) {
			System.out.println("Here you are!");
			balance = balance - price;
			total = total + price;
		}
	}
	
	public static void main(String[] args) {
		VendingMachine vm = new VendingMachine();
		vm.showPrompt();
		vm.showBalance();
		vm.insertMoney(100);
		vm.getFood();
		vm.showBalance();
		
		VendingMachine vm1 = new VendingMachine();
		vm1.insertMoney(200);
		vm.showBalance();
		vm1.showBalance();
	}
}

运行结果

Welcome
0
Here you are!
20
20
200

1.3 成员变量和成员函数

 关于this的使用，在刚才那个程序的基础上，我们修改了一下，注意当中的showPrice()和setPrice（）

package vendingmachine;

public class VendingMachine {
	int price = 80;
	int balance;
	int total;
	
	void setPrice(int price) {
		this.price = price;
	}
	
	void showPrice() {
		System.out.println(this.price);
	}
	
	void showPrompt()
	{
		System.out.println("Welcome");
	}
	
	void insertMoney(int amount) {
		balance = balance + amount;
	}
	
	void showBalance() {
		System.out.println(this.balance);
	}
	
	void getFood() {
		if(balance >= price) {
			System.out.println("Here you are!");
			balance = balance - price;
			total = total + price;
		}
	}
	
	public static void main(String[] args) {
		VendingMachine vm = new VendingMachine();
		vm.showPrice();
		vm.setPrice(55);
		vm.showPrice();

	}
}

 1.4对象初始化

 

package vendingmachine;

public class VendingMachine {
	int price = 80;
	int balance;
	int total;
	
	//构造函数
	VendingMachine(){
		total = 0;
	}
	
	//构造函数
	//重载
	VendingMachine(int price) {
		this.price = price;
	}
	
	void setPrice(int price) {
		this.price = price;
	}
	
	void showPrice() {
		System.out.println(this.price);
	}
	
	void showPrompt()
	{
		System.out.println("Welcome");
	}
	
	void insertMoney(int amount) {
		balance = balance + amount;
	}
	
	void showBalance() {
		System.out.println(this.balance);
	}
	
	void getFood() {
		if(balance >= price) {
			System.out.println("Here you are!");
			balance = balance - price;
			total = total + price;
		}
	}
	
	public static void main(String[] args) {
		VendingMachine vm = new VendingMachine();
		vm.showPrice();
		vm.setPrice(55);
		vm.showPrice();
		
		VendingMachine vm1 = new VendingMachine(100);
		vm1.showPrice();

	}
}

 

1.5 本章练习

package week1;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		Fraction a = new Fraction(in.nextInt(), in.nextInt());
		Fraction b = new Fraction(in.nextInt(),in.nextInt());
		a.print();
		b.print();
		a.plus(b).print();
		a.multiply(b).plus(new Fraction(5,6)).print();
		a.print();
		b.print();
		in.close();
	}
}

class Fraction {
	int up;
	int down;
	
	Fraction(int a,int b){
		this.up = a;
		this.down = b;
	}
	
	double toDouble() {
		return (double)(this.up/this.down);
	}
	
	Fraction plus(Fraction o){
		boolean found = false;
		int num=this.down*o.down;

		int up_new = o.down*this.up +this.down*o.up;
		Fraction fra = new Fraction(up_new,num);
		return fra;
	}
	
	Fraction multiply(Fraction o){
		int up_new = this.up * o.up;
		int down_new = this.down * o.down;
		Fraction fra = new Fraction(up_new,down_new);
		return fra;
	}
	
	void print() {
		if(this.up%this.down ==0) {
			System.out.println(this.up/this.down);
		}
		
		
		
		
		//这里的一个问题是要最简化分式，然后输出
		//自然想到辗转相除法
		//参考
		//int GCD(int a,int b)
		//{    
		//	return b==0?a:GCD(b,a%b);
		//}

		else {
			int a = this.up;
			int b = this.down;
			int c = 0;
			while(b!=0) {
				c = b;
				b = a%b;
				a = c;
			}
			
			System.out.println(this.up/a+"/"+this.down/a);
		}
	}
	
}