Java中的C指针等效

Question

I wanted to know what the Java translation of this block of C code would be.

 Person * father = malloc(sizeof(Person));
 Marriage * marriage = malloc(sizeof(Marriage));
 (* marriage).male = father;

I'm guessing I use reference. So instead of making a variable father point to Person I just make a father object for the class Person like this:

Person father = new Person();

I might be wrong on this.

How would the line (* marriage).male = father; work?

I'm quite new to C and I am just trying to get a better understanding of how it works.

Answer 1

That would be a mere marriage.male = father; in Java.

(*marriage).male is equivalent to marriage->male in C. marriage is a pointer to a memory location, similar to a reference to an object created with new in Java.

Also, note that while in a certain sense those can be associated with Java constructs, they are certainly no "equivalents." Java has a garbage collector, for one. C doesn't. Java is interpreted. C isn't. There's a lot of subtle differences, so I would never say that anything in C is anywhere equivalent to any Java.

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Instead of learning C by equating it with Java, read a book explicitly about C. There are articles like "C for Java programmers" that might be a better entrance for you. However, don't really equate Java with C at all, that just leads to bad stuff.

Answer 2

We can't work with pointers in Java, but, we can translate that code in C to Java:

    Person father = new Person();
    Marriage marriage = new Marriage();
    marriage.male = father;

(* marriage).male = father; is the same that marriage->male = father like cadaniluk said. This operator (* pointer) get the pointer's value, in that case it is a Marriage Object. If you would like to understand better about pointers in C, read this article: Pointers in C

Answer 3

C is a structured but not object-oriented language. There are basically two mechanisms to realize something like objects: data structures called Structs on one side and Pointer on the other side. Pointer are like variables, but made to reference a memory address of a given field.

struct Person {
    char name[50];
};

struct Marriage {
    struct Person *father; /* fields of type 'pointer to a struct person' */
    struct Person *mother; 
} marriage;

int main() {
    struct Person father = {"Steve"};
    marriage.father = &father; /* marriage.father references the memory address of father */
    ...
}

In contrast, Java is an object-oriented language where eg an object A references another object B , without the need for that special pointer type , because these "pointing" happens implicit. So your code example in Java would be:

Person father = new Person(); // acts like struct Person
Marriage marriage = new Marriage(); // acts like struct Marriage
marriage.male = father; // marriage.male references ("points to") father memory address