CODEWITHSUNDEEP
javareflectionmethodsreturnreturn-type
Muhammed Refaat
Muhammed Refaat

Reputation: 9103

how can i know the method return type from only it's name?

I want to know the method return type from only it's name, i'm using that code but it didn't work for me(it always returns null):

public Object getType(String key) throws Exception {

        Object returnType = null;
        String name = key;
        Method[] methods = name.getClass().getMethods();
        for(int i =0; i < methods.length ; i++){
            if(key.equals(methods[i])){
                returnType = methods[i].getReturnType();
            }
        }
        return returnType;
    }

Upvotes: 0

Views: 125

Answers (3)

gawi
gawi

Reputation: 2952

You miss two things. Instead

key.equals(methods[i])

should be:

key.equals(methods[i].getName())

and second thing in my opinion is a class under investigation (your code looks for methods in java.lang.String). So the method should look like:

public Object getType(String methodName, Class<?> clazz) throws Exception {
    String name = methodName;
    Method[] methods = clazz.getMethods();
    for (int i = 0; i < methods.length; i++) {
        if (name.equals(methods[i].getName())) {
            return methods[i].getReturnType();
        }
    }
    return null;
}

and call it like:

type = getType("someMethodName",YourClass.class);

or

type = getType("someMethodName",YourObject.getClass());

Upvotes: 1

Marko Topolnik
Marko Topolnik

Reputation: 200138

Many things are wrong with your attempt; you seem to be arbitrarily chosing methods to invoke, judging intuitively what they do. Please consult the Javadoc of all JDK methods you have never used before.

  1. name.getClass() returns the object reflecting on java.lang.String. You need Class.forName(name);

  2. your whole scheme cannot possibly work if you don't know what class the method is supposed to be the member of. If your string contains both class name and method name, then you need to parse it to tease these two names apart;

  3. klass.getMethods() will only give you the public member methods. This may or may not be what you are after. There is also getDeclaredMethods(), but this one doesn't give you the inherited methods.

Upvotes: 1

Adam Siemion
Adam Siemion

Reputation: 16029

Instead of:

if(key.equals(methods[i])){

you should have

if(key.equals(methods[i].getName())){

Also a small improvement can be made in your code, you do not need the returnType local variable and you do not need to iterate through all the remaining methods when you have already found the method you are looking for, so the code might be:

 public Object getType(String key) throws Exception {
    String name = key;
    Method[] methods = name.getClass().getMethods();
    for(int i =0; i < methods.length ; i++){
        if(key.equals(methods[i])){
            return methods[i].getReturnType();
        }
    }
    return null;
}

Upvotes: 3

Related Questions