What are the common pitfalls and mistakes when using Java functions?

Common Java function pitfalls include: using varargs as the last parameter, ensuring different parameter signatures when overloading methods, ensuring they are constants when using default parameter values, parameter lists and return types must match when overriding methods, Correctly handle checked exceptions.

Common Pitfalls and Mistakes in Java Functions

Trap 1: Variable Parameter List

When using the varargs method, it is critical that it be the last parameter. This is because the compiler will accept any type of argument list, causing unexpected behavior.

public int sum(int... numbers) {
    if (numbers.length == 0) {
        return 0;
    }
    int sum = 0;
    for (int number : numbers) {
        sum += number;
    }
    return sum;
}

Trap 2: Overloading

When overloading methods, make sure they have different parameter signatures. Ambiguous methods may cause compile-time errors or incorrect results.

public int add(int a, int b) {
    return a + b;
}

public int add(int a, float b) {
    return a + b;
}

Trap 3: Default parameter values

When using default parameter values, ensure that the default value is a constant or determined at compile time. Default values ​​cannot be calculated at runtime.

public void printMessage(String message, String format) {
    format = format != null ? format : "Default";
    System.out.println(String.format(format, message));
}

Trap 4: Method Override

When overriding a method, make sure its parameter list and return type match the parent class method. Mismatched signatures can cause compile-time errors.

public class Parent {
    public int calculate(int a, int b) {
        return a + b;
    }
}

public class Child extends Parent {
    @Override
    public float calculate(int a, int b) { // 错误：返回类型不匹配
        return a + b;
    }
}

Trap 5: Checked Exceptions

Java methods can throw two types of exceptions: checked exceptions and unchecked exceptions. When using checked exceptions, you must use a throws clause or wrap it in a try-catch block. Ignoring checked exceptions can result in compile-time errors.

public void readFile() throws IOException { // 抛出已检查异常
    // ... 读文件
}

// 不正确的用法：未正确处理已检查异常
public void readFile() {
    // ... 读文件
}

Practical Case

The following is an example showing how to avoid pitfalls when using variable parameter lists and default parameter values:

public class Example {

    public static int sum(int... numbers) { // 可变参数作为最后一个参数
        int sum = 0;
        for (int number : numbers) {
            sum += number;
        }
        return sum;
    }

    public static void printMessage(String message, String format = "Default") { // 默认参数值为常量
        System.out.println(String.format(format, message));
    }

    public static void main(String[] args) {
        // 调用 sum() 方法，传递可变数量的参数
        System.out.println("总和：" + sum(1, 2, 3, 4, 5));

        // 调用 printMessage() 方法，使用默认格式
        printMessage("你好");

        // 调用 printMessage() 方法，指定自定义格式
        printMessage("欢迎回到 Java", "欢迎：%s");
    }
}

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