Java exceptions (Exceptions) refer to errors or abnormal situations that occur during program running. The Java exception handling mechanism allows the program to handle exceptions when they occur to avoid program crashes or unpredictable errors.
1. The concept of Java exceptions
Java exceptions refer to errors or unusual conditions that occur during program execution. Java exceptions can be divided into two types: compile-time exceptions and run-time exceptions.
Compile-time exceptions refer to exceptions that can be detected during compilation, such as files that do not exist, methods that do not exist, etc. Compile-time exceptions must be handled in the program, otherwise the program cannot be compiled.
Runtime exceptions refer to exceptions that can only be detected while the program is running, such as array out-of-bounds, null pointer reference, etc. Runtime exceptions do not need to be handled, but if not handled, the program will crash or an unpredictable error will occur.
2. Classification of Java exceptions
Java exceptions can be divided into three types: Checked Exception, Unchecked Exception and Error.
Checked Exception refers to a compile-time exception that must be handled in the program, otherwise the program cannot be compiled. Checked Exception is usually caused by code written by the programmer himself, such as the file does not exist, the method does not exist, etc.
Unchecked Exception refers to a runtime exception that does not need to be handled, but if not handled, the program will crash or an unpredictable error will occur. Unchecked Exception is usually caused by programmer errors, such as array out of bounds, null pointer reference, etc.
Error refers to a serious system error, usually caused by system resource exhaustion, virtual machine crash, etc., which cannot be handled by the program.
3. Java exception handling methods
The Java exception handling mechanism allows the program to handle exceptions when they occur to avoid program crashes or unpredictable errors. Java exception handling mechanism includes try-catch-finally statement, throw statement and throws statement.
- try-catch-finally statement
The try-catch-finally statement is used to catch and handle exceptions. The try block contains code that may throw exceptions, the catch block is used to catch exceptions and handle them, and the finally block is used to release resources or perform cleanup operations.
try { // Code that may throw an exception } catch (Exception e) { // Exception handling code } finally { // Release resources or perform cleanup operations }
- throw statement
The throw statement is used to manually throw exceptions. You can customize the exception type and throw it in the program.
public void test() throws Exception { throw new Exception("custom exception information"); }
- throws statement
The throws statement is used to declare the types of exceptions that a method may throw and can be used in method declarations.
public void test() throws Exception { // Code that may throw exceptions }
4. Things to note about Java exception handling
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Don't overuse try-catch-finally statements, and avoid exceptions as much as possible.
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Runtime exceptions should be avoided as much as possible in programs, and compile-time exceptions or custom exceptions should be used.
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When handling exceptions, exception information should be recorded in as much detail as possible to facilitate subsequent debugging and repair.
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When using the try-catch-finally statement, exception types should be captured and processed according to the inheritance relationship from small to large.
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When using the throw statement, you should use Java's built-in exception types whenever possible and avoid using custom exception types.
Summarize
Java exceptions are errors or unusual conditions that occur during program execution. Java exceptions can be divided into two types: compile-time exceptions and run-time exceptions. The Java exception handling mechanism allows the program to handle exceptions when they occur to avoid program crashes or unpredictable errors. When handling exceptions, exception information should be recorded in as much detail as possible to facilitate subsequent debugging and repair.