1. Exception types
The main difference between checked exceptions and unchecked exceptions lies in their handling methods. Checked exceptions need to be processed by the compiler using the try, catch and finally keywords, otherwise a compiler error will occur. This is not necessary for unchecked exceptions. All exceptions in Java classes that inherit Exception are checked exceptions, and all exceptions that inherit RuntimeException are called unchecked exceptions.
2. ClassCastException
Class conversion exception. This exception will be thrown when converting an instance that is not of this class into this class.
If you force a number into 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 will be thrown when operating the 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());
Tips: Once an exception occurs in the program and is not handled, execution will be terminated.
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