Beginners - Exception

abnormal

An anomaly is a not a normal event in the course of running the program in what happened, it would interrupt the running program

JAVA Exception Handling

Five keywords exception handling

• try
• catch
• finally
• throw
• throws

Exception object commonly used method

Common types of exceptions

 

Multiple catch blocks

Arrangement catch statement order: first subclass of the parent class
when an abnormality occurs in sequence one by matching
only the first will match the type of abnormality of catch statement

    
        the catch (a InputMismatchException E) { // subclass EDITORIAL 
            System.out.println ( "enter an integer" ); 
            e.printStackTrace (); 
        } the catch (Exception E) { // parent written on the back 
            System.out.println ( "input error" ); 
            e.printStackTrace (); 
        } 
        a finally { 
            System.out.println ( "open to suggestions" ); // there are no exceptions regardless of program output 
        }

 

throw与throws 

Exception Handling Principles

异常处理与性能
异常只能用于非正常情况
不要将过于庞大的代码块放在try中
在catch中指定具体的异常类型
需要对捕获的异常做处理

异常结构图

异常链

 

//新建两个自定义Exception类
public class FkException extends Exception{//第一个自定义付款类
//重写Exception里的两个方法
    public FkException(String message, Throwable cause) {
        super(message, cause);
        // TODO Auto-generated constructor stub
    }

    public FkException(String message) {
        super(message);
        // TODO Auto-generated constructor stub
    }

}
//第二个自定义购物车类
class GwException extends Exception{
    public GwException(String message, Throwable cause) {
        super(message, cause);
        // TODO Auto-generated constructor stub
    }

    public GwException(String message) {
        super(message);
        // TODO Auto-generated constructor stub
    }


}

//新建一个购物车的类方便传参数
public class Gwc {
    private String shangpin;
    private int money;
    public String getShangpin() {
        return shangpin;
    }
    public void setShangpin(String shangpin) {
        this.shangpin = shangpin;
    }
    public int getMoney() {
        return money;
    }
    public void setMoney(int money) {
        this.money = money;
    }

}

//新建一个购物车的方法把建好的Gwc类当参数放进去
public static void gwc(Gwc gwcs) throws GwException {
        if(gwcs==null){
            throw new GwException("购物车不能为空");//抛出异常
        }else{
            System.out.println("添加成功");
        }
    }

//在新建一个付款类继续抛出一个异常

public static void fukuan(Gwc gwcs) throws FkException{
try {
gwc(gwcs);

} catch (GwException e) {
e.printStackTrace();
throw new FkException("付款不能为0");

}
}

//我们去main方法里去调用写的方法
public static void main(String[] args) {
        Gwxt s=new Gwxt();
        try {
            s.fukuan(null);
        } catch (Exception e) {
            e.printStackTrace();
        }
}
//下图则是控制台打印出来的结果，可以看到并没有关联起来，我们可以修改一下
    

public static void fukuan(Gwc gwcs) throws FkException{
        try {
            gwc(gwcs);
            
        } catch (GwException e) {
            e.printStackTrace();    
            throw new FkException("付款不能为0",e);
            //修改之后的代码，把e添加到抛出的异常里
        }
    }
//如下就是我们想要的结果了

 

 

小提示

printStackTrace();打印异常堆栈信息

exit(1)  退出虚拟机

try-catch块中存在return语句，是否还执行finally块? 如果执行，说出执行顺序？

先执行finally然后再回去执行return

try-catch- finally块中， finally块唯一不执行的情况是什么？

exit(1) 

try-catch-finally结构中try语句块是必须的，catch、finally语句块均可选，但两者至少出现之一