1.java.lang.nullpointerexception

Everyone must encounter this exception frequently. The explanation of the exception is "the program encountered a null pointer." Pointer" simply means calling an uninitialized object or a non-existent object. This error often occurs in operations such as creating pictures and calling arrays. For example, the picture is not initialized, or the path when creating the picture is wrong, etc. .

The occurrence of null pointers in array operations is often a mistake made by friends who are just beginning to learn programming, that is, confusing the initialization of the array with the initialization of the array elements. The initialization of the array is to allocate the required space to the array. However, the elements in the initialized array have not been instantiated and are still empty, so each element needs to be initialized.

2, java.lang.classnotfoundexception

This exception is caused by many programmers who originally developed in jb and other development environments. They put the packages under jb in wtk A common problem that occurs during compilation is that the explanation of the exception is "the specified class does not exist".

The main consideration here is whether the name and path of the class are correct. If the package is made under jb, package is usually added by default, so after switching to wtk, pay attention to the package. path added.

3, java.lang.arithmeticexception

The explanation of this exception is "mathematical operation exception". For example, an operation such as division by zero will occur in the program. For such an exception, everyone should carefully check the mathematical operations involved in their program to see if there is something wrong with the formula.

4, java.lang.arrayindexoutofboundsexception

I believe many friends have often encountered this exception. The explanation of the exception is "array index out of bounds". Now in the program Most of them operate on arrays, so when calling an array, you must check carefully to see if the subscript you are calling exceeds the range of the array.

Generally speaking, explicit calls are not prone to such errors, but implicit calls often make errors. There is another situation where the length of the array defined in the program is determined by certain specific methods. , is not declared in advance. At this time, it is best to check the length of the array to avoid this exception.

5, java.lang.illegalargumentexception

The explanation of this exception is "method parameter error". Many methods in j2me class libraries will in some cases Triggering such an error, for example, if the volume parameter in the volume adjustment method is written as a negative number, this exception will occur. Therefore, once you find this exception, you must quickly check whether there is an error in the parameter passing in the method call.

6, java.lang.illegalaccessexception

The explanation of this exception is "no access permission". When the application wants to call a class, but the current method does not This exception will occur when accessing this class. Please pay attention to this exception when using packages in the program.

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