Java特定contains()逻辑咨询及字符串存入Vector代码相关问题

Hey Karen, let's break down this method first since it's core to your question. Since you're using Vector (which implements the Collection interface), contains() works exactly as defined for all standard collections in Java:

• Core Behavior: The contains(Object o) method checks if the collection holds an element that is "equal" to the input o. The key here is that equality is determined by the element's equals() method—not reference equality (==), unless the element type hasn't overridden equals() (like a raw custom class).
• For Your String Use Case: Since String overrides equals() to compare actual text content, calling vkCode.contains("KEY_ENTER") will return true if any element in the vector matches that exact string. This is almost certainly what you're expecting!
• Custom Object Heads-Up: If you ever store custom objects in these vectors, you must override both equals() and hashCode() in your class. Without this, contains() will only check if the object reference matches the one you pass in, which is rarely useful.

Looking at your snippet, you're reading lines from code.txt, splitting them by #, and populating two vectors. Let's fix some potential issues and make the code more robust:

1. Resource Leak Risk #

Your current code calls abc.close() inside the try block, but if an exception is thrown before that line (like during readLine()), the reader won't close properly. Use try-with-resources (Java 7+) to auto-manage resources—it's cleaner and safer.

2. Array Index Out-of-Bounds Risk #

When you split a line with split("#"), if a line doesn't contain a #, the resulting array will only have one element. Trying to access split[1] would crash your code. Always check the array length first.

3. Cleaned-Up Code Example #

Here's a revised version of your method that addresses these issues:

public void readCode() {
    // Assuming lines, vkCode, vkName are declared as Vector<String> elsewhere
    try (BufferedReader abc = new BufferedReader(new FileReader("code.txt"))) {
        String line;
        while ((line = abc.readLine()) != null) {
            lines.add(line);
            String[] split = line.split("#");
            // Validate the split result before accessing elements
            if (split.length >= 2) {
                vkCode.add(split[0]);
                vkName.add(split[1]);
            } else {
                // Handle invalid lines (adjust this based on your needs)
                System.err.println("Skipping malformed line: " + line);
            }
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
        // Optional: Add a user-friendly message like "Could not locate code.txt"
    } catch (IOException e) {
        e.printStackTrace();
        // Optional: Handle read errors (e.g., corrupted file)
    }
}

4. Quick Side Note: Vector vs. ArrayList #

Vector is thread-safe, but if your code doesn't need thread safety (e.g., you're only modifying these collections in a single thread), ArrayList is more efficient. The contains() method works identically for both, so switching won't break your logic.

内容的提问来源于stack exchange，提问作者Karen