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How to write code that performs actions based on what type

Please bear with me as I am struggling to explain this issue. So let's say I have a custom type called "UserType" and that this type has 4 values: North, South, East, and West.

public enum UserType {
    NORTH, SOUTH, EAST, WEST
}

Then I want to write a method statement in another class that will increment the value of two variables based on the type. For example,

public class direction {
    private int peopleWhoGoNorth;
    private int peopleWhoGoSouth;

therefore peopleWhoGoNorth has to keep track of the number of people who go north each time the following method is called:

public void whichWay(UserType type) {
        }

I'm wondering how I would create a statement between the parentheses that basically says, if type North, add 1 to peopleWhoGoNorth, and if type is South, add 1 to peopleWhoGoSouth. I assume the if / else statement should do this, but I'm not sure how the syntax will work. Is the following OK?

public void whichWay (UserType type){
    if (UserType = NORTH){peopleWhoGoNorth = peopleWhoGoNorth + 1);
    if (UserType = SOUTH){peopleWhoGoSouth = peopleWhoGoSouth + 1);
    }

Please let me know if there is a way to explain the question.

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6 answers


You can use a switch for enums:



public void whichWay (UserType type){
  switch (type) {
    case NORTH:
      peopleWhoGoNorth++;
      break;
    case SOUTH:
      peopleWhoGoSouth++;
      break;
    default:
      throw new IllegalArgumentException();
  }
}
+4


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You need to use ==

: if (type == NORTH)

.

You can also use the operator switch

:



switch(type) {
  case NORTH: 
    peopleWhoGoNorth++;
    break;
  case SOUTH: 
    peopleWhoGoSouth++;
    break;
  default: // do nothing
}
+3


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You can just compare yours type

with the types you want to test.

public void whichWay(UserType type) {
    if (type == UserType.NORTH) {
        //Execute code
    }
    //Other types analog
}

or you can use a switch statement:

public void whichWay(UserType type) {
    switch (type) {
        case NORTH:
            //Execute code
            break;
        //Other types analog
        default:
    }
}
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I would say that you are on the right track.

Let's consider only the "whichWay" method:

public void whichWay(UserType type) {
    if(type == UserType.NORTH) { peopleWhoGoNorth++; }
    else if(type == UserType.SOUTH) { peopleWhoGoSouth++; }
}
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switch

and if-else

, but you can also use Map

to keep a counter of those who left in a given direction.

public enum UserType {
    NORTH, SOUTH, EAST, WEST
}

public class Example{
    private final Map<UserType,Integer> typeMap = new HashMap<>();

    public void whichWay(UserType type){
        int val = typeMap.getOrDefault(type,0);
        typeMap.put(type,val++);
    }
}

Of course, you will need to add methods to get these values ​​to make this useful.

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One option would be to use EnumMap :

private final EnumMap<UserType, Integer> counter = new EnumMap<> (UserType.class);
{
  for (UserType u : UserType.values()) counter.put(u, 0);
}

public void whichWay (UserType type){
  counter.put(type, counter.get(type) + 1);
}

Or with Java 8:

private final EnumMap<UserType, Integer> counter = new EnumMap<> (UserType.class);

public void whichWay (UserType type){
  counter.compute(type, (u, i) -> i == null ? 0 : i + 1);
}

(Note: this is not thread safe)

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