Exception

 

 

 Exception  分两种： 编译时异常和RuntimeException.

编译时异常必须要处理。

异常处理的五个关键字：throw,throws,try..catch,finally

1.使用throw抛出异常：

 

NullPointerException和 ArrayIndexOutOfBoundsException 都是运行时异常。

    public static void main(String[] args) {
        int[] arr = null;
        int value = getElement(arr, 0);
        System.out.println(value);
    }
    
    public static int getElement(int[] arr,int index) {
        if(arr == null) {
            throw new NullPointerException("The array is null!");
        }
        if(index<0||index>arr.length-1) {
            throw new ArrayIndexOutOfBoundsException("Index out of bounds:"+index);
        }
        int value = arr[index];
        return value;
    }

Exception in thread "main" java.lang.NullPointerException: The array is null!
    at exception.TestThrow.getElement(TestThrow.java:14)
    at exception.TestThrow.main(TestThrow.java:8)

 2.使用throws处理异常：

 

 

 

 3.使用try...catch处理异常

4.finally

    public static void main(String[] args) {
        int[] arr  = null;
        int index = 0;
        try {
            int value = getElement(arr, index);
            System.out.println("Get value: "+value);
            return;
        } catch (Exception e) {
            System.out.println(e);
            return;
        }finally {
            System.out.println("finally里面的代码");//这段代码都会打印出来
        }        
    }
    
    public static int getElement(int[] arr,int index) {
        if(arr == null) {
            throw new NullPointerException("The array is null!");
        }
        if(index<0||index>arr.length-1) {
            throw new ArrayIndexOutOfBoundsException("Index out of bounds:"+index);
        }
        int value = arr[index];
        return value;
    }

 

 如果finally里面有return语句，那么永远返回finally里面的结果。（要尽量避免该情况）

 

自定义异常：