Java - Java有类似C＃的struct自动构造函数

Question

I've been using C# for a long time and now I need to do something in Java.

Is there something like C#'s struct automatic constructor in java ?

What I mean is In C#

struct MyStruct
{
    public int i;
}
class Program
{
    void SomeMethod()
    {
        MyStruct mStruct; // Automatic constructor was invoked; This line is same as MyStruct mStruct = new MyStruct();
        mStruct.i = 5;   // mStruct is not null and can i can be assigned
    }
}

Is it possible to force java to use default constructor on declaration ?

Answer 1

No - Java doesn't support custom value types at all, and constructors are always explicitly called.

However, your understanding of C# is incorrect anyway. From your original post:

// Automatic constructor was invoked
// This line is same as MyStruct mStruct = new MyStruct();
MyStruct mStruct; 

That's not true. You can write to mStruct.i without any explicit initialization here, but you can't read from it unless the compiler knows everything has been assigned a value:

MyStruct x1; 
Console.WriteLine(x1.i); // Error: CS0170: Use of possibly unassigned field 'i'

MyStruct x1 = new MyStruct();
Console.WriteLine(x1.i); // No error

Answer 2

No, you always need to explicitly call a constructor in Java.

Since there may be multiple constructors, calling a specific constructor explicitly would probably be good practice anyway.

Answer 3

Java不支持Struct关键字（请参阅： http ： //msdn.microsoft.com/en-us/library/ms228600 （v = VS.90 ） .aspx ）因此您需要使用仅公开的类对象（没有函数。）你总是需要初始化类。