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1. What are variable length parameters?
Variable Arguments is a feature in Java, also called varargs. It allows methods to accept an unlimited number of parameters.
In Java, we usually need to specify the parameter types and number of methods. But sometimes, we want to be able to flexibly pass any number of parameters to a method without having to determine the number of parameters in advance. This is where variadic parameters come in.
2. Why do we need variable length parameters?
Using variable-length parameters can simplify the code and make the method more flexible. Variable-length parameters provide a convenient way to handle situations when we are not sure how many parameters a method needs to receive.
In the absence of variable-length parameters, if we want to achieve similar functionality, we may need to define multiple overloaded methods, each method accepting a different number of parameters. This leads to code redundancy and increases maintenance costs.
3. How to implement variable length parameters?
The implementation principle of variable-length parameters is to store the incoming parameters through an array. Inside the method, we can operate on the variable-length parameter as an array.
In Java, the syntax for variable-length parameters is expressed by using three consecutive dots (...) in the method declaration. For example:
public void method(String... args) {
// 方法体
}
In the above code, argsit is a string array that can receive any number of string parameters.
When we call a method with variable length parameters, we can pass any number of parameters, or even no parameters. The compiler will encapsulate these parameters into an array and pass it to the method.
4. Examples of using variable length parameters
Here is a simple example demonstrating how to use variable length parameters:
public class VarargsExample {
public static void main(String[] args) {
printNumbers(1, 2, 3);
printNumbers(4, 5, 6, 7, 8);
printNumbers(); // 不传递任何参数
}
public static void printNumbers(int... numbers) {
for (int number : numbers) {
System.out.println(number);
}
}
}
In the above code, printNumbersthe method accepts variable-length parameters numbersand prints out all the numbers through an enhanced for loop iteration.
The output is:
1
2
3
4
5
6
7
8
5. Advantages of variable length parameters
-
简化代码：可变长参数允许我们在方法声明中指定一个参数，而不需要提前确定参数的个数。 -
灵活性：可以传递任意数量的参数，包括零个参数。
6. 可变长参数的缺点
-
可能引发歧义：如果同时存在多个重载方法，其中一个方法接受可变长参数，另一个方法接受数组参数，那么在调用时可能会引发歧义。
7. 可变长参数的使用注意事项
-
可变长参数必须是方法的最后一个参数。 -
可变长参数只能出现一次，并且必须放在参数列表的最后。
8. 总结
可变长参数是 Java 中的一种特性，允许方法接受不定数量的参数。它通过数组来存储传入的参数，并提供了简化代码和灵活性的优点。但需要注意避免与其他重载方法产生歧义。
参考资料
首发博客地址: https://blog.zysicyj.top/
[2]面试题手册: https://store.amazingmemo.com/chapterDetail/1685324709017001
[3]系列文章地址: https://blog.zysicyj.top/categories/技术文章/后端技术/系列文章/面试题精讲/
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