自动为变量生成某些方法

Question

I have a question of how, if possible, one can generate methods automatically by only providing variable of a spefic kind.

Let's illustrate my question with simple example: Assuming I have multiple variables linked to LinkedLists and I would like to give each certain methods; for example setters and getters methods:

private LinkedList football = new LinkedList();
private LinkedList jogging = new LinkedList();

public LinkedList getFootball() {
    return football;
}
public void setFootball(LinkedList football) {
    this.football = football;
}
public LinkedList getJogging() {
    return jogging;
}
public void setJogging(LinkedList jogging) {
    this.jogging = jogging;
}

If number of variables gets long (example only contains 2), this will produce very long and rather repetetive peace of code, illustrated above.

Is there any way, if this is indeed a possability, to generalize the above pattern so I can create both methods by just creating an instance of LinkedList?

PS: using foreach loop and generalizing it for arbitrary element does NOT WORK.

Answer 1

You might be looking for Lombok :

You can annotate any field with @Getter and/or @Setter, to let lombok generate the default getter/setter automatically.

A default getter simply returns the field, and is named getFoo if the field is called foo (or isFoo if the field's type is boolean).

In your case, this class

@Getter
@Setter
public class MyClass {
    private LinkedList football = new LinkedList();
    private LinkedList jogging = new LinkedList();
}

would lead to the following code:

public class MyClass {
    private LinkedList football = new LinkedList();
    private LinkedList jogging = new LinkedList();

    public LinkedList getFootball() {
        return football;
    }

    public void setFootball(LinkedList football) {
        this.football = football;
    }

    public LinkedList getJogging() {
        return jogging;
    }

    public void setJogging(LinkedList jogging) {
        this.jogging = jogging;
    }
}

However, Lombok requires some compiler configuration , so while you're at it, you might as well consider to check out Kotlin , where your class can be written simply as this:

class MyClass {
    var football = LinkedList<Any?>()
    var jogging = LinkedList<Any?>()
}

Answer 2

You can't do that at run-time. However, a lot of IDE:s have an option to autogenerate getters and setters.

For instance in Eclipse, you open the context menu with a left click and look under "Source", or press Alt + Shift + s to open the source menu. There you'll find an option labeled "Generate Getters and Setters", that will open a dialog button that lets you choose what setters and getters to create, where to insert them in the code etc..

Answer 3

You are asking for various sorts of trouble with code readability, optimizations and loss of encapsulation, not to mention losing compile-time checks for correct variable names. Regardless, you can create a generic setter and getter (in this case for LinkedLists) through reflection like this:

 public void setter(String name, LinkedList value) throws IllegalArgumentException {
    try {
      Field field = getClass().getDeclaredField(name);
      field.setAccessible(true);
      field.set(this, value);
      field.setAccessible(false);
    } catch (NoSuchFieldException | IllegalAccessException e) {}
  }

  public LinkedList getter(String name) {
    LinkedList ret = null;
    try {
      Field field = getClass().getDeclaredField(name);
      field.setAccessible(true);
      Object object = field.get(this);
      if (object instanceof LinkedList) {
        ret = (LinkedList) object;
      }
      field.setAccessible(false);
    } catch (NoSuchFieldException | IllegalAccessException e) {
      e.printStackTrace();
    }
    return ret;
  }

Answer 4

Why not use a map to organize your lists? I made up a runnable example for you:

import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;

public class ListsManager {

    Map<String, LinkedList<String>> lists;

    public static void main(String[] args) {
        ListsManager lm = new ListsManager();
        System.out.println(lm.getList("football"));
    }

    public ListsManager(){
        //initialize map
        lists = new HashMap<String, LinkedList<String>>();
        //add lists
        lists.put("football", new LinkedList<String>());
        lists.put("jogging", new LinkedList<String>());
        //fill lists with objects
        lists.get("football").add("football 1");
        lists.get("football").add("football 2");
        lists.get("jogging").add("jogging 1");
        lists.get("jogging").add("jogging 2");
    }

    public void setList(String id, LinkedList list){
        lists.put(id, list);
    }

    public LinkedList getList(String id){
        return lists.get(id);
    }

}

This way you can address the lists via an ID. The example prints [football 1, football 2]

EDIT: I used lists of strings - of course you can change the generics to whatever you want.

Answer 5

If you need something like this, I'd suggest you use the Apache DynaBean . It is essentially a Wrapper around a Map. But this is only really sensible if you don't know the properties of your bean at compile time.