For exceptions in the program, it is a situation that many programmers do not want to see, because this requires us to query the cause of the exception, and then perform some operations to handle the exception. In Java array operations, there will be some exceptions. Here we have listed two types: ClassCastException and NullPointerException, let's take a look at the specific introduction.
1. Types of abnormalities
The main difference between checked and unchecked exceptions lies in the way they are handled. Checked exceptions need to be handled by the compiler using try, catch and finally keywords, otherwise the compiler will report an error. This is not necessary for unchecked exceptions. All exceptions of classes that inherit Exception in Java are checked exceptions, and all exceptions that inherit RuntimeException are called unchecked exceptions.
2、ClassCastException
Class conversion exception. Converting an instance of this class to this class will throw this exception.
If a number is forcibly converted to a string, this exception will be reported:
Object x = new Integer(0);
System.out.println((String)x);
This is a runtime exception and does not need to be caught manually.
3. NullPointerException
This exception is thrown when manipulating a method or property of a null object.
//情况一：
int[] arr1 = new int[]{1,2,3};
arr1 = null;
System.out.println(arr1[0]);
//情况二：
int[][] arr2 = new int[4][];
System.out.println(arr2[0][0]);
//情况：
String[] arr3 = new String[]{"AA","BB","CC"};
arr3[0] = null;
System.out.println(arr3[0].toString());
Prompt: Once the program is abnormal and has not been dealt with, the execution will be terminated.
Content expansion:
- Arithmetic exception class: ArithmeticExecption
- Null pointer exception class: NullPointerException
- Type casting exception: ClassCastException
- Array negative subscript exception: NegativeArrayException
- Array subscript out of bounds exception: ArrayIndexOutOfBoundsException
- Violation of the safety principle exception: SecturityException
- File has ended exception: EOFException
- File not found exception: FileNotFoundException
- String conversion to number exception: NumberFormatException
- Operation database exception: SQLException
- Input and output exception: IOException
- Method not found exception: NoSuchMethodException
