如何在java中为特定构造函数创建方法？

Question

When I create a method in Java, that method applies to every instance of the class, no matter which constructor I use to create that instance. What I want to know is how can I a method be invoked only by instances created by a specific constructor of my choosing.

/** (that program below is just an example of my point) */
public class Person{
        private int height;

        /** first constructor */
        public Person(){
            height = 0;
        }

        /** second constructor */
        public Person(int height){
            this.height = height;
        }

        /** I want this method to work just on the constructor with the int parameter   */
        public void getTaller(){
             height = height + 1;
        }

}

Answer 1

The closest to what you're asking is inheritance and factory methods:

public class Person {
    public static Person createWithoutHeight() {
        return new Person();
    }

    public static Person createWithHeight(int height) {
        return new PersonWithHeight(height);
    }
}

public class PersonWithHeight extends Person {
    private int height;

    public PersonWithHeight(int height) {
        this.height = height;
    }

    public void makeTaller() {
        height++;
    }
}

Answer 2

在Java中没有这样的东西，你不能创建一个方法并选择这个方法到特定的构造函数。

Answer 3

You cannot limit the use of methods on an instance regardless of which constructor is used. Read about what an instance is. The getTaller will just increment the height which can start at 0 or the specified height.

Answer 4

Split the class into an abstract class and two implementations:

public abstract class Person {
    protected int height;
    protected Person(int height) {
        this.height = height
    }
    public int getHeight() {
        return height;
    }
}

public class PersonImmutable extends Person {
    public PersonFixed(int initialHeight) {
        super(initialHeight)
    }
}

public class PersonMutable extends Person {
    public PersonFixed(int initialHeight) {
        super(initialHeight)
    }
    public void setHeight(int newHeight) {
        this.height = newHeight;
    }
}

Answer 5

I believe what OP is trying to put a function pointer as a parameter to a constructor. Unfortunately, unlike C/C++, Java does not allow such things , as there is no such thing as a function pointer in Java.

On the other hand, you could make use of a light Command pattern , that is, you encapsulate a function through an object.

Example:

class Function {
    // fields here, each stands for a function parameter
    public Function ( insert params here ) {
        // initialize your Function object here
    }

    // the meat of it
    public void execute() {
        // do whatever your function should do
    }
}

Then in your constructor, add your Function as a parameter to it, as in

public Person(Function myFunction) {
    // do whatever you want here
    // ...
    // then you call your custom function
    myFunction.execute();
}

This is the most generic behavior of passing a function as parameter to another function. You may, of course, tweak this to your heart's content (add parameters to the execute() method, etc).