零基础学JAVA DAY13

 今天是周一，和平常一样没什么特殊的事情发生。下午在闲鱼上买了一部小米5作为测试机，希望能不被坑，也就用这个来测试一下开发的应用罢了，没指望它能有多大的用途。今天学了JAVA的异常处理和io流的一部分知识，时而学习时而摸鱼？哎，还是感觉非常的尴尬啊，自己在那里一坐废物的一批。我和导师说自己写不出来那个APP，也不知道他到底听进去了吗。还让我写那个根本就没思路啊。不说了，想过了年就辞职去考雅思，也不知道家里会不会同意这件事情呢，说出来怕不是要被毒打。就这样，明天继续加油

package homework;
/**
 * 假设有一个方法 public int method()， 会返回一个整数
 * 在这个方法中有try catch 和 finally.
 * try 里返回 1
 * catch 里 返回 2
 * finally 里 返回 3
 * 那么，这个方法到底返回多少？
 */

import java.io.File;
import java.io.FileInputStream;

public class Test {
    public static void main(String[] args) {
        System.out.println(method());
    }
    private static int method(){
        try {
            return 1;
        } catch (Exception e) {
            e.printStackTrace();
            return 2;
        }
        finally {
            return 3;
        }
    }
}

Throwable是类，Exception和Error都继承了该类，所以在捕捉的时候，也可以使用Throwable进行捕捉
如图： 异常分Error和Exception，Exception里又分运行时异常和可查异常。

package homework;
/**
 * 在方法声明上，可以抛出指定的异常，比如FileNotFoundException
 * 那么能否抛出Throwable这个类？ 
 *
 * 这个方法的调用者又该如何处理？
 */

import java.io.File;
import java.io.FileInputStream;

public class Test {
    public static void main(String[] args) {
        try{
            throwmethod();
        } catch (Throwable throwable) {
            throwable.printStackTrace();
        }

    }
    private static void throwmethod() throws Throwable{
        File f = new File("d:/LOL.exe");

        System.out.println("试图打开 d:/LOL.exe");
        new FileInputStream(f);
        System.out.println("成功打开");
    }
}

package homework;
/**
 * 练习-异常综合1
 */
public class Account {
    private double balance;
    public Account(double balance) {
        this.balance = balance;
    }
    public double getBalance(){
        return balance;
    }
    public void deposit(double addBalance){
        balance = balance + addBalance;
    }
    public void withdraw(double minusBalance) throws OverDraftException{
        if (balance - minusBalance < 0){
            throw new OverDraftException("余额不足", minusBalance - balance);
        }
        balance = balance - minusBalance;
    }

}

package homework;

public class OverDraftException extends Exception {
    //deficit为透支
    private double deficit;
    public double getDeficit() {
        return deficit;
    }
    public OverDraftException(String msg, double deficit) {
        super(msg);
        this.deficit = deficit;
    }
}

package homework;


public class Test {
    public static void main(String[] args) {
        //开户存了1000
        Account a = new Account(1000);
        //存钱1000
        a.deposit(1000);
        //查看余额
        System.out.println(a.getBalance());

        try {
            //取2001
            a.withdraw(2001);
        } catch (OverDraftException e) {
            System.err.println("透支金额："+e.getDeficit());
            e.printStackTrace();
        }

    }
}

package homework;
/**
 * 练习-异常综合2
 */
public class CheckingAccount extends Account {
    //此属性代表透支额度
    private double overdraftProtection;
    public CheckingAccount(double balance) {
        super(balance);
    }
    public CheckingAccount(double balance,double overdraftProtection){
        super(balance);
        this.overdraftProtection = overdraftProtection;
    }
    @Override
    public void withdraw(double minusBalance) throws OverDraftException{
        if (minusBalance > balance + overdraftProtection){
            double deficit = minusBalance - balance - overdraftProtection;
            throw new OverDraftException("透支额度超标", deficit);
        }
        balance = balance - minusBalance;
    }
}

package homework;

public class Test {
    public static void main(String[] args) {
        //开户存了1000块，拥有500的透支额度
        CheckingAccount a = new CheckingAccount(1000, 500);
        //存了1000
        a.deposit(1000);
        //查询余额
        System.out.println(a.getBalance());
        try {
            a.withdraw(600);
            System.out.println(a.getBalance());
            a.withdraw(600);
            System.out.println(a.getBalance());
            a.withdraw(600);
            System.out.println(a.getBalance());
            a.withdraw(600);
            System.out.println(a.getBalance());
            a.withdraw(600);
            System.out.println(a.getBalance());
        } catch (OverDraftException e) {
            System.err.println("透支超额:" + e.getDeficit());
            e.printStackTrace();
        }

    }
}