java新手笔记9 类的封装示例

1.bank类

package com.yfs.javase;
//类封装
public class BankCard {

	//属性
	int balance;//默认0  实例变量 分配给每个对象一个
	//String name;

	// 方法 存钱
	public void saveMoney(int   money) {
		if(money < 0) {
			System.out.println("非法操作...");
			return;
		}
		System.out.println("向账户存入" + money +"元...");
		balance += money;
	}

	//取钱  调用时传入参数
	public void drawMoney(int money) {
		//验证余额
		if(balance < money) {
			System.out.println("账户余额不足...");
			return; //终止方法调用
		}

		 System.out.println("从账户取出" + money + "元...");
		 balance -= money;
	}

}

2.测试

package com.yfs.javase;

public class CardTest {

	public static void main(String[] args) {
//		  BankCard bc1 = null;//声明引用
//		  bc1 = new BankCard();//创建对象
		  BankCard bc1 = new BankCard();
		  System.out.println("银行卡余额：" + bc1.balance);
		  bc1.drawMoney(200);//调用对象方法

		  bc1.saveMoney(5000);

		  bc1.drawMoney(500000);

		  bc1.drawMoney(500);

		  bc1.saveMoney(-500);
		  System.out.println("银行卡余额：" + bc1.balance);

	}

}

3.测试1

package com.yfs.javase;

public class CardTest2 {

	public static void main(String[] args) {

		  BankCard bc1 = new BankCard();
		  System.out.println("银行卡余额：" + bc1.balance);
		  bc1.saveMoney(5000);
		  bc1.drawMoney(500);
		  System.out.println("银行卡余额：" + bc1.balance);

		  BankCard bc2 = new BankCard();
		  System.out.println("银行卡余额：" + bc2.balance);
		  bc2.saveMoney(3000);
		  System.out.println("bc2银行卡余额：" + bc2.balance);
		  System.out.println("bc1银行卡余额：" + bc1.balance);

	}

}

4.测试2

package com.yfs.javase;

public class CardTest3 {

	public static void main(String[] args) {

		  BankCard bc1 = new BankCard();
		  bc1.saveMoney(5000);
		  bc1.drawMoney(500);
		  System.out.println("银行卡余额：" + bc1.balance);

		  BankCard bc2 = new BankCard();
		  bc2.saveMoney(3000);
		  System.out.println("bc2银行卡余额：" + bc2.balance);
		  bc2.drawMoney(5000);
		  bc2.balance = 10000;//修改余额  不安全操作
		  bc2.drawMoney(5000);
		  System.out.println("bc2银行卡余额：" + bc2.balance);

	}

}

1.1bank类

package com.yfs.javase.update;
//类封装
public class BankCard {

	//属性  private 属性私有  只能在当前类中访问
	private int balance;// 实例变量 分配给每个对象一个
	private int password;

	// 方法 存钱
	public void saveMoney(int   money) {
		if(money < 0) {
			System.out.println("非法操作...");
			return;
		}
		System.out.println("向账户存入" + money +"元...");
		balance += money;//在方法中访问
	}

	//取钱  调用时传入参数
	public void drawMoney(int money) {
		//验证余额
		if(balance < money) {
			System.out.println("账户余额不足...");
			return; //终止方法调用
		}

		 System.out.println("从账户取出" + money + "元...");
		 balance -= money;
	}
	//通过访问balance属性方法 不能修改
	public void  getBalance () {
		System.out.println("账户余额：" + balance);
	}

}

2.1测试

package com.yfs.javase.update;

public class CardTest3 {

	public static void main(String[] args) {

		  BankCard bc1 = new BankCard();
		  bc1.saveMoney(5000);
		  bc1.drawMoney(50000);
//		  bc1.balance = 100000000;//编译出错
//		  System.out.println("银行卡余额：" + bc1.balance);//私有属性不能访问

		  bc1.getBalance();
		 // bc1.password;

	}

}

3.1方法重载条件

package com.yfs.javase.update;

import java.util.Random;

public class Demo2 {
//	public int add(int a, int b) {
//		return a + b;
//	}
    //变量名称不能成为重载条件
//	public int add(int c , int d) {
//		return c + d;
//	}
	public double add(int a , double b) {

		return a + b;

	}
	//返回值类型不能成为重载条件
	public long add( int a, int b) {

		return a + b;
	}
	public static void main(String[] args) {
		Demo2 d1 = new Demo2();
		long val = d1.add(1,6);

	}

}

4.1方法重载示例

package com.yfs.javase.update;

public class OverRideDemo {
	//方法的重载  方法使用相同的名字
	public int add (int a, int b) {
		 return a + b;
	}

	public  int  add (int a , int b, int c) {
		return a + b + c;
	}

	public double add( double a, double b) {
		return a + b;
	}
	public static void main(String[] args) {
		//创建对象
		OverRideDemo od = new OverRideDemo();
		int val = od.add(3,5);
		System.out.println("add(3,5) = " + val);

		val = od.add(3,5,8);//根据调用时传入参数个数 类型匹配对应方法
		System.out.println("add1(3,5,8) = " + val);

		double result = od.add(3.14, 2.71);
		System.out.println("add(3.14, 2.71) = " + result);

	}

}