Exception handling in Java

Java is an object-oriented programming language. Due to its high stability and security, it has become a widely used programming language. However, in the process of program development, exceptions are always inevitable problems. Since the Java language is inherently capable of handling exceptions, it can use the exception handling mechanism to avoid program crashes and ensure the normal operation of the program.

1. Overview of exceptions in Java

In Java, exceptions refer to abnormal situations that occur in the program, such as array out-of-bounds, divisor is zero, file not found, etc. However, these exceptions will not directly cause the program to crash like C language, but will throw an exception object. This object can be defined by the programmer, or it can be an existing exception class in Java, such as NullPointerException (null pointer exception), ArrayIndexOutOfBoundsException (array subscript out-of-bounds exception), etc.

When an exception occurs in the program, the Java virtual machine will search for the appropriate exception handler when the exception is thrown, discover and call the relevant handler to handle the exception, if not found, the program will throw Exception, the system will finally end the execution of the program. In Java, exceptions are handled through try-catch-finally statement blocks.

2. Exception handling in Java

The exception handling mechanism in Java can be divided into the following two situations:

1. Exception is not handled

When the exception in the program is not included in the try-catch statement block, or the exception is not caught in the try statement block, and the exception is thrown directly, the program will crash. In order to avoid this situation from happening, we can catch exceptions through the throws keyword or try-catch statement block.

2. Exception is handled

When the exception in the program is successfully caught, we can choose to handle the exception or throw a new exception object. If you handle exceptions, you can use try-catch statement blocks. If you throw a new exception object to replace the original exception, you can use the throw statement.

3. Exception catching methods in Java

There are two main ways to catch exceptions in Java, namely try-catch statement block and throws keyword. Both methods can effectively handle exceptions, as follows:

1. try-catch statement block

try-catch statement block is used to catch exceptions in Java One of the methods is mainly used to handle small-scale exceptions. The specific usage is as follows:

try{

// 可能会抛出异常的代码块

} catch(Exception e) {

// 捕获异常后的处理代码块

} finally{

// 这里的代码块无论如何都会执行

}

The try statement block contains code that may throw exceptions, and the catch statement block is used to catch and handle thrown exceptions. If the code in the try block does not throw an exception, the catch block will not execute. The finally statement block is used to execute code that needs to be executed anyway, such as resource closing operations, etc.

2. throws keyword

Thethrows keyword is a method of handling exceptions in Java, mainly used to handle a wide range of exceptions. When a method throws an exception, you can use the throws keyword at the declaration of the method to declare the exception. At this time, the compiler will check whether there is a statement to handle the exception in the method, and if not, an error will be reported.

For example:

public void read(String fileName) throws IOException {

BufferedReader reader = new BufferedReader(new FileReader(fileName));
String line;
while ((line = reader.readLine()) != null) {
    System.out.println(line);
}
reader.close();

}

In the above code, the method read() may Throws an IOException. At this time, we can use the throws keyword at the method declaration to declare that the method may throw the exception.

4. Exception classes in Java

There are two basic exception classes in Java, namely RuntimeException and CheckedException. RuntimeException refers to exceptions that may be thrown when the program is running. These exceptions are not forced to be handled during compilation and will only be thrown when they occur at runtime, such as NullPointerException, ArrayIndexOutOfBoundsException, etc. CheckedException refers to exceptions that will not be thrown when the program is running. Programmers must explicitly handle exceptions when writing code, such as IOException, SQLException, etc.

In addition to these two basic exception classes, there are also custom exception classes in Java. The creation of custom exception classes helps make code more readable and maintainable. Custom exception classes generally inherit from the Exception or RuntimeException class and override some constructors to customize the exception type.

5. Precautions for exception handling in Java

When handling exceptions in Java, there are also some things to pay attention to:

1. Exceptions should be caught as early as possible or Throw, this can avoid some unnecessary time-consuming operations.
2. When using try-catch statement blocks to handle exceptions, try to avoid excessive nesting, and the code structure should be simple and clear.
3. When handling exceptions, you should handle them according to the type of exception, rather than simply using a catch statement block to catch all exception types.
4. When performing exception handling, exception information should be handled correctly. In order to facilitate debugging and logging, the details of the exception information should be output.

In short, exception handling is a very important part of Java development. Reasonable exception handling can avoid program crashes and ensure the normal operation of the program; it can also facilitate debugging and provide guarantee for later maintenance and upgrades.

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