how do you bind a function in hashmap

Question

Lets say for example we are gonna bind the function into a hashmap

if(identity.equals("printf")){
    doPrintf(statement);
}else if(identity.equals("scanf")){
    doScanf(statement);
}else if(identity.equals("puts")){
    doPuts(statement);
}else if (identity.equals("functioncall")){
    expectFunc  = true;
}else if (identity.equals("functioncallwithparams")){
    expectFunc  = true;
    expectParams = true;
}else if (identity.equals("assignment")){
    //doAssignment(statement);
    vartoupdate = statement;
    updateVar = true;
}else if(identity.equals("getch"))
    doGetch();

something like this HM.put("getch",doGetch()). How could you possibly do this?

http://stackoverflow.com/questions/2882948/calling-a-method-named-string-at-runtime-in-java-and-c Is this what you want to do? — Ramon Marco L. Navarro, Jan 17 '12 at 08:14

score 3 · Answer 1 · edited May 23 '17 at 10:34

3

If I get your question correctly, you want to call a method based on its name (or at least part of it). If so, you should look at the reflection API, there's a related question here on SO btw: How do I invoke a Java method when given the method name as a string?

edited May 23 '17 at 10:34

Community

1
1

answered Jan 17 '12 at 07:27

Savino Sguera

3,442
20
20

score 2 · Answer 2 · answered Jan 17 '12 at 07:27

If you can take the hit for creating a new object for each function, this can simply be achieved by creating a Function object for each function to be called and maintaining a mapping between the function name and it's corresponding function object.

public interface Function<T> {    
   public T apply(Object... vargs);    
}

Now just make every function object implement this interface, create new objects for each newly created class and stuff them in a map.

score 2 · Answer 3 · answered Jan 17 '12 at 07:27

interface Func { 
    public void exec();
}

class GetCharFunc implements Func { 
   @Override
   public void exec() { 
       // implementation details
   }
}

Func currentFunc;

if(identity.equals("getch")) {
    currentFunc = new GetCharFunc();
    myMap.put("getch", currentFunc); 
}

score 2 · Answer 4 · answered Jan 17 '12 at 07:28

2

You could do it if all the functions implemented the same Interface. Which doesn't seem to be the case for you.

answered Jan 17 '12 at 07:28

user949300

15,154
6
33
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score 1 · Answer 5 · answered Jan 17 '12 at 07:29

Java does not support references to methods or functions as a language feature. You can either create a interface with one method and implement this multiple times with your different method invocations or use Reflection and put the java.lang.reflect.Method objects into your hash map.

score 1 · Answer 6 · answered Jan 17 '12 at 07:34

If you're using Java 7, you can use a switch statement based on a String value. Here's a brief tutorial on that: Use String in the switch statement with Java 7

If Java 7 isn't an option I think the next best option is to switch on an enum. Here's a tutorial on enum types.

Perhaps if you explained what problem you're trying to solve you'd get better answers.

how do you bind a function in hashmap

6 Answers6