How to use finally in java

The finally block in Java is used to ensure that the code will be executed after the try-catch statement block is completed, regardless of whether an exception occurs. Common uses include releasing resources, performing cleanup operations, and recording errors. It executes after the try or catch block, has no access to local variables, and has execution priority higher than the return statement.

Usage of finally in Java

In Java, the finally block is an integral part of the exception handling mechanism . It ensures that some code is executed after the try-catch block completes, regardless of whether an exception occurs.

Purpose

The finally block is usually used in the following situations:

• Release resources:Release file connections, databases connection or other external resource.
• Perform cleanup operations: Close the stream, clear the collection, or reset the variable.
• Logging errors: Record exception information to a log or other data structure.

Syntax

The syntax of the finally block is as follows:

try {
    // 要尝试执行的代码
} catch (Exception exception) {
    // 处理异常
} finally {
    // 无论是否出现异常，都执行的代码
}

Execution order

finally Blocks are always executed after a try or catch block. If no exception occurs in the try block, the finally block will be executed immediately after the try block. If an exception occurs in the try block, the finally block will be executed immediately after the catch block.

Note

• Unable to access local variables: finally blocks cannot access local variables in try or catch blocks because these variables Will be destroyed after the end of these blocks.
• Return value: If the finally block returns a value, it will overwrite the value returned by the try or catch block.
• Avoid infinite loops: Avoid using infinite loops or recursive calls in finally blocks, as this can lead to program deadlock.
• Priority higher than return: The execution priority of the finally block is higher than the return statement, which means that the finally block is executed before the return statement.

Example

The following example shows how to release a file connection:

BufferedReader reader = null;
try {
    reader = new BufferedReader(new FileReader("file.txt"));
    // 读取文件
} catch (IOException exception) {
    // 处理异常
} finally {
    if (reader != null) {
        reader.close();
    }
}

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