第2课第5节_Java面向对象编程_异常_P

 

java的异常处理的原则如下:

1、我们先写一个没有对异常处理的程序，在进行除法运算的时候，除数是非零的话，运行时没有问题的，但是除数为零的时候，运行就会有问题，程序也不能往下执行(只打印了Begin of div)

public class Div{

    public static void main(String args[]){
        int m = Integer.parseInt(args[0]);
        int n = Integer.parseInt(args[1]);

        System.out.println("Begin of div");
        int r = div(m,n);
        System.out.println("end of div");

        System.out.println(m+"/"+n+"="+r);
    }

    public static int div(int m,int n){
        int r = m / n;
        return r;
    }
}

 2、我们先写一个有对异常进行处理程序(自己处理异常)，根据下面的运行结果，程序可以捕获到异常并且可以正常的执行.

public class Div2{

    public static void main(String args[]){
        int m = Integer.parseInt(args[0]);
        int n = Integer.parseInt(args[1]);

        System.out.println("Begin of div");
        int r = div(m,n);
        System.out.println("end of div");

        System.out.println(m+"/"+n+"="+r);
    }

    public static int div(int m,int n){
        int r = 0;
        try {
            r = m / n ;
        }catch (ArithmeticException e){
            System.out.println(e);
        }finally{
            System.out.println("This is finally of div");
        }

        return r;
    }
}

3、我们写一个程序将异常抛出的类，这个抛出的异常是由main进行处理.

public class Div4{

    public static void main(String args[]){
        int m = Integer.parseInt(args[0]);
        int n = Integer.parseInt(args[1]);
        int r = 0;

        System.out.println("Begin of div");
        try {
            r = div(m,n);
        }catch (ArithmeticException e){
            System.out.println(e);
        }
        System.out.println("end of div");

        System.out.println(m+"/"+n+"="+r);
    }

    public static int div(int m,int n) throws ArithmeticException{
        int r = 0;
        
        r = m / n ;

        return r;
    }
}

 4、如果在类的方法中如果处理了异常，那样在main方法中就不会对异常进行处理.

public class Div5{

    public static void main(String args[]){
        int m = Integer.parseInt(args[0]);
        int n = Integer.parseInt(args[1]);
        int r = 0;

        System.out.println("Begin of div");
        try {
            r = div(m,n);
        }catch (ArithmeticException e){
            System.out.println(e);
        }
        System.out.println("end of div");

        System.out.println(m+"/"+n+"="+r);
    }

    public static int div(int m,int n) throws ArithmeticException{
        int r = 0;

        try{
            r = m / n ;
        }catch(ArithmeticException e){
            System.out.println("div :"+e);
        }

        return r;
    }
}

5、如果在类的方法中如果处理了异常，同时在类方法中把异常抛出，那样main方法也可以捕获到异常.

public class Div6{

    public static void main(String args[]){
        int m = Integer.parseInt(args[0]);
        int n = Integer.parseInt(args[1]);
        int r = 0;

        System.out.println("Begin of div");
        try {
            r = div(m,n);
        }catch (ArithmeticException e){
            System.out.println(e);
        }
        System.out.println("end of div");

        System.out.println(m+"/"+n+"="+r);
    }

    public static int div(int m,int n) throws ArithmeticException{
        int r = 0;

        try{
            r = m / n ;
        }catch(ArithmeticException e){
            System.out.println("div :"+e);
            throw e;
        }

        return r;
    }
}

6、现在我们上面第5个例子的代码，只有对这种算术运行的异常进行处理，如果我传入的参数个数不对，还有参数的格式也不对，程序是处理不了的。

为了修复上述的问题，我们添加对传入参数格式不对，还有传入参数个数不对这两种异常的处理。

public class Div7{

    public static void main(String args[]){
        int m = 0;
        int n = 0;
        int r = 0;

        System.out.println("Begin of div");
        try {
            m = Integer.parseInt(args[0]);
            n = Integer.parseInt(args[1]);
            r = div(m,n);
        }catch (ArithmeticException e){
            System.out.println("main :" + e);
        }catch (NumberFormatException e){
            System.out.println("main :" + e);
        }catch (ArrayIndexOutOfBoundsException e){
            System.out.println("main :" + e);
        }
        System.out.println("end of div");

        System.out.println(m+"/"+n+"="+r);
    }

    public static int div(int m,int n) throws ArithmeticException{
        int r = 0;

        try{
            r = m / n ;
        }catch(ArithmeticException e){
            System.out.println("div :"+e);
            throw e;
        }

        return r;
    }
}

7、在第6个例子继续优化，上面的程序目前只能对算术运算、参数格式还有参数个数不对的异常进行处理，其他的情况是无法处理的到的，我们可以添加对这些异常的父类RuntimeException来捕获异常.

public class Div8{

    public static void main(String args[]){
        int m = 0;
        int n = 0;
        int r = 0;

        System.out.println("Begin of div");
        try {
            m = Integer.parseInt(args[0]);
            n = Integer.parseInt(args[1]);
            r = div(m,n);
        }catch (ArithmeticException e){
            System.out.println("main :" + e);
        }catch (NumberFormatException e){    //去掉了参数个数的异常，仍然可以捕获到
            System.out.println("main :" + e);
        }catch (RuntimeException e){
            System.out.println("main :" + e);
        }
        System.out.println("end of div");

        System.out.println(m+"/"+n+"="+r);
    }

    public static int div(int m,int n) throws ArithmeticException{
        int r = 0;

        try{
            r = m / n ;
        }catch(ArithmeticException e){
            System.out.println("div :"+e);
            throw e;
        }

        return r;
    }
}

8、对于“不可查异常”, 系统也会抛出它，写不写throws效果一样

public class Div9{

    public static void main(String args[]){
        int m = 0;
        int n = 0;
        int r = 0;

        System.out.println("Begin of div");
        try {
            m = Integer.parseInt(args[0]);
            n = Integer.parseInt(args[1]);
            r = div(m,n);
        }catch (ArithmeticException e){
            System.out.println("main :" + e);
        }catch (NumberFormatException e){
            System.out.println("main :" + e);
        }catch (RuntimeException e){
            System.out.println("main :" + e);
        }
        System.out.println("end of div");

        System.out.println(m+"/"+n+"="+r);
    }

    //public static int div(int m,int n) throws ArithmeticException{
    public static int div(int m,int n){
        int r = 0;

        try{
            r = m / n ;
        }catch(ArithmeticException e){
            System.out.println("div :"+e);
            throw e;
        }finally{
            System.out.println("finally of div");
        }

        return r;
    }
}