Varying the order of method calling for different instances of a class

Question

What is the best way of manipulating the order things are done based on some conditions (other than writing them again with the different order)?

Let's say there is a Person class and each object of Person represents a different human.

class Person{
    int eatingPriority = 3;
    int sleepingPriority = 2;
    int recreationPriority = 1;

    void eat() {/*eats*/}
    void sleep() {/*sleeps*/}
    void watchTv() {/*watches tv*/}

    void satisfyNeeds() {
        //HOW TO DO THIS
    }
}

How can I make the satisfyNeeds() methods call the other three methods based on their priority?

Note: I want to make it clear that priorities can change from Person to Person.

Answer 1

You can do this with 1 class and 1 interface.

public class Person {
    int eatingPriority = 3;
    int sleepingPriority = 2;
    int recreationPriority = 1;

    PriorityQueue<Action> actions;

    void eat() { }

    void sleep() { }

    void watchTv() { }

    public Person() {
        actions = new PriorityQueue<Action>(new Comparator<Action>() {
            @Override
            public int compare(Action o1, Action o2) {
                return o2.getPriority() - o1.getPriority();
            }
        });

        actions.add(new Action() {
            @Override
            public int getPriority() {
                return eatingPriority;
            }
            @Override
            public void execute() {
                eat();
            }
        });

        actions.add(new Action() {
            @Override
            public int getPriority() {
                return sleepingPriority;
            }
            @Override
            public void execute() {
                sleep();
            }
        });

        actions.add(new Action() {
            @Override
            public int getPriority() {
                return recreationPriority;
            }
            @Override
            public void execute() {
                watchTv();
            }
        });
    }

    public void satisfyNeeds() {
        for (Action action : actions) {
            action.execute();
        }
    }

    interface Action {
        public int getPriority();
        public void execute();
    }
}

Answer 2

Here is another possible implementation :

abstract class Need {
  abstract void satisfy();
}

class Eat extends Need {
  @Override
  public void satisfy() { /* eat ...*/}
}

class Sleep extends Need {
  @Override
  public void satisfy() { /* sleep ...*/}
}

class DrinkBeer extends Need {
  @Override
  public void satisfy() { /* drink beer ...*/}
}

class Person{
  // TreeMap will sort the map in the key's natural order (a int here)
  private Map<Integer, Need> needs = new TreeMap<>();    

 Person() {
   add(new Eat(), 3);
   add(new Sleep(), 2);
   add(new DrinkBeer(), 1);
 }

 void add(Need need, int priority) {
   needs.put(Integer.valueOf(priority), need);
 }

 void satisfyNeeds() {
    for(Need need : needs.values())
      need.satisfy();
  }
} 

Answer 3

This solution would require Java 8:

class Person {

    void eat() {};
    void sleep() {};
    void watchTv() {};

    // Being in a List you can easily reorder the needs when you want to
    List<Runnable> needs = Arrays.asList(this::eat, this::sleep);

    // Alternatively, you can use a Map<Runnable, Integer> where the value is your
    // priority and sort it (see http://stackoverflow.com/q/109383/1296402)

    void satisfyNeeds() {
        needs.forEach(Runnable::run);
    }
}

Answer 4

You can use this code

import java.util.Arrays;  // must be imported
int[] priorities = {sleepPriority, eatPriority, recreationPriority};
Arrays.sort(priorities);
for (int i=priorities.length-1; 0<=i; i--) {
    int priority = priorities[i];
    if (priority == sleepingPriority) { sleep(); }
    if (priority == eatingPriority) { eat(); }
    if (priority == recreationPriority) { watchTv(); }
}

Basically, it puts the priorities in an array, sorts the array and runs a for loop on it to run the functions.

Answer 5

Finding the right order of three elements can be done simply like this:

 void satisfyNeeds() {
     boolean eatFirst = eatingPriority>Math.max(sleepingPriority,recreationPriority);
     if(eatFirst) eat();
     if(sleepingPriority>recreationPriority) {
         sleep();
         watchTv();
     }
     else {
         watchTv();
         sleep();
     }
     if(!eatFirst) eat();
  }

Of course, it won’t scale if you raise the number of actions. For a higher number you might look at one of the other answers.

Answer 6

You should introduce a map property into Person class, where prioritize methods, for example:

class Person {

...
private Map<Integer, Method> methodsPriority = new HashMap<>();
...
 public Person setEatingPriority(int priority) {

  methodsPriority.put(priority, /* put 'eat' method reference here*/);
  return this;
 }

 public Person setSleepingPriority(int priority) {

  methodsPriority.put(priority, /* put 'sleep' method reference here*/);
  return this;
 }

 public Person setWatchingTVPriority(int priority) {

  methodsPriority.put(priority, /* put 'watch TV' method reference here*/);
  return this;
 }

 public void satisfyNeeds() {

  Collection<Integer> keys = methodsPriority.keySet();
  Collections.sort(keys);
  for(Integer key: keys)
   methodsPriority.get(key).invoke(this);
 }



...
}

And it can be used in next manner:

Person Anna = new Person()
.setEatingPriority(1)
.setSleepingPriority(2)
.setWatchingTVPriority(3);

Person Bob = new Person()
.setEatingPriority(3)
.setSleepingPriority(2)
.setWatchingTVPriority(1);

Anna.satisfyNeeds();
Bob.satisfyNeeds();