Java - How to define a variable with variable type

Question

I have to declare a variable, the type of this variable depends on a parameter, so I have an if clause and define this variable there:

if(this.httpMethod == "POST"){
    HttpPost request = new HttpPost(url);
}
if(this.httpMethod == "GET"){
    HttpGet request = new HttpGet(url);
}

The problem is that in Java, the scope of that variable lies inside the if, so I can't use it later !. If I try:

request.addHeader("Accept", "application/json");

That gives me: request cannot be resolved

So, the question would be: how can I define a variable, that it's type depends on a parameter.

What I have tried:

Setting the variable to final.

My current solution is to duplicate the code, inside every if clause, I set the same Headers, Connection, grab the response, .... So, of course, I don't like this.

Design. I have this HTTP request class like this, so I can use it to handle the request, so, I just have to send it some parameters (URL, method, authentication, ...) , and it will give me back the result. This class is my bottom layer of my Android app, that looks like this:

Activities.java (all the activities)
Core.java (handle resources)
HttpRequest.java (handle internet resources)

if(this.httpMethod.equals("POST")). use .equals to compare strigns — Raghunandan
– Raghunandan, Commented May 19, 2014 at 17:31
@Raghunandan Thanks for remind me that. I will change it. Although my question still open... — Francisco Corrales Morales
– Francisco Corrales Morales, Commented May 19, 2014 at 17:40

Badgerati · Accepted Answer · 2014-05-19 17:38:47Z

1

Both HttpPost and HttpGet inherit HttpRequestBase. So you can declare the request variable outside the if statement like so:

HttpRequestBase request = null;

if (this.httpMethod.equals("POST")) {
   request = new HttpPost(url);
}
else if (this.httpMethod.equals("GET")) {
   request = new HttpGet(url);
}

request.addHeader(...); etc

answered May 19, 2014 at 17:38

Badgerati

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1 Comment

Francisco Corrales Morales Over a year ago

I just tested this. Works perfect. Thanks for the explanation also.

ashishduh · Accepted Answer · 2014-05-19 17:37:38Z

0

You should declare a variable of both variable types' superclass outside the if statements. Example:

Superclass object;

if (condition){
    object = new Subclass1();
}
else {
    object = new Subclass2();
}

answered May 19, 2014 at 17:37

ashishduh

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1 Comment

Francisco Corrales Morales Over a year ago

Thank you, I think you meant like this: stackoverflow.com/a/23743896/2615737

Dave Newton · Accepted Answer · 2014-05-19 18:34:56Z

0

You need to declare the variable to be of the supertype outside of the if blocks and then use it inside them:

        HttpRequestBase request = null;

        if("POST".equals(this.httpMethod)){
            request = new HttpPost(url);
        }
        else if("GET".equals(this.httpMethod)){
            request = new HttpGet(url);
        }

And then later in your code when you're ready to use it, be sure to check whether the request is null or not.

Edited based on changes to the original question

edited May 19, 2014 at 18:34

Dave Newton

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answered May 19, 2014 at 17:35

Carl Anderson

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5 Comments

Francisco Corrales Morales Over a year ago

I can't, Java won't let me change the type of a variable.

Dave Newton Over a year ago

This sidesteps the important issue, though, because in the code you're skipping the difference between the two methods.

Carl Anderson Over a year ago

I just realized you had a typo in your posted code and were setting two different subtypes.

Francisco Corrales Morales Over a year ago

I edited my question. Yes, that answer work. Thank you. stackoverflow.com/a/23743896/2615737

Carl Anderson Over a year ago

Edited my answer to be correct as well. Please note that the "GET".equals(this.httpMethod) style will not throw a NullPointerException if httpMethod is null.

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