java - 在 Java 中将数组作为方法参数传递

Question

以下代码使用 Java 中的简单字符串数组。

package javaarray;

final public class Main
{
    public void someMethod(String[] str)
    {
        System.out.println(str[0]+"\t"+str[1]);
    }
    public static void main(String[] args)
    {
        String[] str1 = new String[] {"day", "night"};
        String[] str2 = {"black", "white"};

        //Both of the above statements are valid.

        Main main=new Main();
        main.someMethod(str1);
        main.someMethod(str2);

        //We can invoke the method someMethod by supplying both of the above arrays alternatively.

        main.someMethod(new String[] { "day", "night" }); //This is also valid as obvious.
        main.someMethod({ "black", "white" }); //This is however wrong. The compiler complains "Illegal start of expression not a statement" Why?
    }
}

在上面的代码片段中，我们可以像这样初始化数组。

String[] str1 = new String[] {"day", "night"};
String[] str2 = {"black", "white"};

我们可以直接将它传递给一个方法，而无需像这样分配。

main.someMethod(new String[] { "day", "night" });

如果是这样，那么下面的说法也应该有效。

main.someMethod({ "black", "white" });

但是编译器提示“表达式的非法开始不是语句”为什么？

Answer 1

根据 Java 语言规范 (10.6. Array Initializers)

An array initializer may be specified in a declaration, or as part of an array creation expression (§15.10), creating an array and providing some initial values:

因此，只有两种方法可以使用数组初始值设定项 ({"foo", "bar"}):

1. 变量声明:String[] foo = {"foo", "bar"};
2. 数组创建表达式:new String[] {"foo", "bar"};

您不能将数组初始值设定项用作方法参数。

15.10. Array Creation Expressions

ArrayCreationExpression:    new PrimitiveType DimExprs Dimsopt    new ClassOrInterfaceType DimExprs Dimsopt    new PrimitiveType Dims ArrayInitializer     new ClassOrInterfaceType Dims ArrayInitializer