异常处理的动手动脑

Posted 2021-01-18 xcl666

一，抛异常的类型

抛异常：1,Error错误，系统错误 2,Exception错误
Exception类又包括：RuntimeException非检查异常和检查异常。
Error例子: 1.AssertionError程序运行期间判断某个条件是否满足
,不满足时，抛出AssertionError。

                 2.OOM Error系统内存不足。

二，小探索

int i=1, j=0, k;
k=i/j;

javac生成idiv字节码指令
double d1=100,d2=0,result;
    result=d1/d2;
System.out.println("浮点数除以零：" + data);

浮点数除以0：Infinity
javac生成ddiv字节码指令，JVM在具体实现这两个指令时，采用了不同的处理策略，导致两段代码运行时得到不同的结果。

三，try catch的嵌套

public class CatchWho { 
    public static void main(String[] args) { 
        try { 
                try { 
                    throw new ArrayIndexOutOfBoundsException(); 
                } 
                catch(ArrayIndexOutOfBoundsException e) { 
                       System.out.println(  "ArrayIndexOutOfBoundsException" +  "/内层try-catch"); 
                }
 
            throw new ArithmeticException(); 
        } 
        catch(ArithmeticException e) { 
            System.out.println("发生ArithmeticException"); 
        } 
        catch(ArrayIndexOutOfBoundsException e) { 
           System.out.println(  "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 
        } 
    } 
}

ArrayIndexOutOfBoundsException/内层try-catch
发生ArithmeticException

上述是结果

public class CatchWho2 { 
    public static void main(String[] args) { 
        try {
                try { 
                    throw new ArrayIndexOutOfBoundsException(); 
                } 
                catch(ArithmeticException e) { 
                    System.out.println( "ArrayIndexOutOfBoundsException" + "/内层try-catch"); 
                }
            throw new ArithmeticException(); 
        } 
        catch(ArithmeticException e) { 
            System.out.println("发生ArithmeticException"); 
        } 
        catch(ArrayIndexOutOfBoundsException e) { 
            System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 
        } 
    } 
}

ArrayIndexOutOfBoundsException/外层try-catch

看下面这段代码，

public class EmbededFinally {

    
    public static void main(String args[]) {
        
        int result;
        
        try {
            
            System.out.println("in Level 1");

           
             try {
                
                System.out.println("in Level 2");
                    //result=100/0;  //Level 2
               
                 try {
                   
                     System.out.println("in Level 3");
                      
                     result=100/0;  //Level 3
                
                } 
                
                catch (Exception e) {
                    
                    System.out.println("Level 3:" + e.getClass().toString());
                
                }
                
                
                finally {
                    
                    System.out.println("In Level 3 finally");
                
                }
                
               
                // result=100/0;  //Level 2

            
                }
            
            catch (Exception e) {
               
                 System.out.println("Level 2:" + e.getClass().toString());
           
             }
             finally {
                
                System.out.println("In Level 2 finally");
           
             }
             
            // result = 100 / 0;  //level 1
        
        } 
        
        catch (Exception e) {
            
            System.out.println("Level 1:" + e.getClass().toString());
        
        }
        
        finally {
           
            System.out.println("In Level 1 finally");
        
        }
    
    }

}

运行结果为

in Level 1
in Level 2
in Level 3
Level 3:class java.lang.ArithmeticException
In Level 3 finally
In Level 2 finally
In Level 1 finally

当有多层嵌套的finally时，异常在不同的层次抛出    ，在不同的位置抛出，会导致不同的finally语句块执行顺序。

四，自定义异常

Class MyException extends Exception
    { …    }
Class MyClass {
        void someMethod() {
            if (条件) throw new MyException();
        }
    }