How to nest methods in java to force user to use the nested name?

Question

I'm writing a library, for more readability I want to force user to use nested methods to call the correct functions.

For example this is my class looks like:

public class Foo{
public void methodA(){}
public void methodB(){}
public void methodC(){}
}

What I'm expecting the user:

Foo foo = new Foo();
foo.methodA.methodB();
foo.methodA.methodC();

to call method B & C through calling the methodA as a prefix

https://stackoverflow.com/questions/2872222/how-to-do-method-chaining-in-java-o-m1-m2-m3-m4. See this link — Vivek Mishra, Jul 02 '19 at 05:07

Intsab Haider · Answer 1 · 2019-07-02T06:52:09.190

2

After reading your question i think you are asking about Builder Design patten in which every methods return type is same class object and you can make call hierarchy like this.

obj.aMethod().bMethod().cMethod();

in your example just do like this:

public class Foo{
 private static final Foo instance = new Foo();
 private Foo(){}

 public static Foo getInstance(){
    return instance;
 }

 public Foo methodA(){
  //Do stuff 
  return getInstance();
 }
 public Foo methodB(){}
 public Foo methodC(){}
}

Now you can call like objfoo.getInstance().methodA().methodB();

Hope it will help you. To read more about that pattern

edited Jul 02 '19 at 06:52

answered Jul 02 '19 at 06:21

Intsab Haider

3,491
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Thanks but this is not builder pattern. I'm trying to force user so he/she can't call methodB directly and has to go through methodA – Mohammad Hossein Kalantarian Jul 02 '19 at 07:34
Oh OK then you have to return object of same class in methodA and then you can call any method with that method. – Intsab Haider Jul 02 '19 at 07:45

score 0 · Answer 2 · answered Jul 02 '19 at 05:33

This is called as method chaining. You will need to set the return type of all methods as the same as the Class.

public class Foo{ 
public Foo methodA()
public Foo methodB() 
public Foo methodC() 
}

Now the client can simply call:

foo.methodA().methodB(), etc.

You can have one "terminal method" i.e. one that does not return a value. For example

public void methodD();

This method will be called last.

foo.methodA().methodB().methodC().method();

This line in itself will be valid as return type is void.

Please look at method chaining/ builder pattern YouTube videos, it will be clear.

Turo · Accepted Answer · 2019-07-02T06:20:43.497

0

To force the user to use methodA to access methodB you could use an inner class. In methodB you can access the Foo-Object with Foo.this.

public class Foo{
   public Bar methodA()
   {
       // ...
       return new Bar();
   }

   public class Bar {

      private Bar() {}; // only methodA can create a Bar object

      public void methodB(){}
      public void methodC(){}

  } 
}

edited Jul 02 '19 at 06:20

answered Jul 02 '19 at 06:08

Turo

4,724
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How to nest methods in java to force user to use the nested name?

3 Answers3