Parsing variadic parameters for advanced usage in Java

Advanced usage analysis of Java variable parameters

In Java, variable parameters are a flexible and powerful feature that allows methods to accept an indefinite number of parameters. . This article explains the advanced use of variadic parameters and provides code examples to aid understanding.

The basic usage of variable parameters is very simple. You only need to use three dots (...) in the method parameter list to represent variable parameters. For example, the following method can accept a variable number of integer parameters:

public static void sumAll(int... numbers) {
    int sum = 0;
    for (int num : numbers) {
        sum += num;
    }
    System.out.println("Sum: " + sum);
}

When calling this method, you can pass any number of integer parameters, such as:

sumAll(1, 2, 3);  // 输出：Sum: 6
sumAll(10, 20, 30, 40);  // 输出：Sum: 100

However, the usage of variable parameters is far more complicated. It doesn't stop there. Several advanced uses are introduced below.

1. Combined use of variable parameters and ordinary parameters

Variable parameters can be used together with ordinary parameters, but it should be noted that variable parameters must be placed in the parameter Last on the list. For example:

public static void printInfo(String name, int age, String... hobbies) {
    System.out.println("Name: " + name);
    System.out.println("Age: " + age);
    System.out.println("Hobbies:");
    for (String hobby : hobbies) {
        System.out.println("- " + hobby);
    }
}

When calling this method, you can pass one or more hobby parameters:

printInfo("Alice", 25, "reading", "swimming");
printInfo("Bob", 30, "playing chess");

2. Restrictions on variable parameters of the same type

Can Variable parameters can only accept parameters of the same type. If you try to pass parameters of different types, the compiler will report an error. For example:

public static void printNumbers(int... numbers) {
    for (int num : numbers) {
        System.out.println(num);
    }
}

public static void printInfo(String... info) {
    for (String str : info) {
        System.out.println(str);
    }
}

// 错误用法示例：
printNumbers(1, 2, 3.0);  // 编译错误：不同类型的参数不允许
printInfo("Name", 25, "Hobby");  // 编译错误：不同类型的参数不允许

3. Variable parameter air conditioning uses

You can also call the variable parameter method without passing any parameters. At this point, the variadic argument will be treated as an empty array. For example:

public static void printNames(String... names) {
    if (names.length == 0) {
        System.out.println("No names");
    } else {
        for (String name : names) {
            System.out.println(name);
        }
    }
}

printNames();  // 输出：No names

4. Multiple overloaded methods with variable parameters

If there are multiple overloaded methods at the same time, one of them uses variable parameters, and the other methods use normal Parameters, you need to pay attention to the matching of method calls. The Java compiler will choose the most exact matching method possible. For example:

public static void printInfo(String name) {
    System.out.println("Name: " + name);
}

public static void printInfo(String... names) {
    for (String name : names) {
        System.out.println("Name: " + name);
    }
}

printInfo("Alice");  // 输出：Name: Alice
printInfo("Bob", "Charlie");  // 输出：Name: Bob 
 Name: Charlie

Variable parameters are a flexible and powerful feature in Java. Mastering its advanced usage can enable us to write more flexible methods. Through the analysis and code examples of this article, I hope readers can have a deeper understanding of variable parameters and be able to use them flexibly in actual development.

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