Variables in Constructor?

Question

I am currently a beginner in Java programming and was tasked to "Code and test a version of the Hangman game. Your solution will involve a Hangman class whose constructor chooses a word, and whose guess method processes each guessed character."

However, I have one little problem. My entire code works and compiles and I have already written the guess method, but I have a problem compiling. I declare my instance variables inside of my constructor. I use the String variable word in my code at various places, and it does not let me compile.
The heart of my problem is this.

public class Hangman{

public Hangman () {

    String word = "p u m p k i n";
    String blanks = "_ _ _ _ _ _ _";


}
 int k = word.length(); ... rest code after this

When I try to compile this, it does not let me. It says that variable word is null and displays an error message. Why can't I use word.length() to find the value of the length? Is it not possible to use the variables declared inside of the constructor as instance variables? The easiest workaround to this is to declare my instance variables outside of the constructor (my code works flawlessly if I do), but the prompt wants me to choose the declare the word inside the constructor.Why can't I use the String word that I declared as "p u m p k i n" inside of the constructor to get k? Using the variable blanks inside of my method does not work either.

So, what is wrong with this? How can I use the variables declared in the constructor as instance variables? Or is this not possible? Why can't I use the String word or String blanks declared in the constructor? Thanks.

Variables declared in any function are local to that function and their scope is in that function only. So there is no question of using variables declared in constructor as instance variables. You can declare instance variables and initialize them inside your constructor. — Aniket Thakur
– Aniket Thakur, Commented Nov 22, 2013 at 7:19

Suresh Atta · Accepted Answer · 2013-11-22 07:45:18Z

5

Each time you are creating the local variables in constructor.

public Hangman () {

    String word = "p u m p k i n";
    String blanks = "_ _ _ _ _ _ _";


}

What you have to do is Assign values in constructor to the members.

    String word;
    String blanks;
    public Hangman () {
        word = "p u m p k i n";
        blanks = "_ _ _ _ _ _ _";

    }

More over it doesn't make sense that not getting them in constructor args and assign them in constructor.

It should be

 public Hangman (String word, String blanks) {
                        this.word   = word;
                        this.blanks = blanks;

                    }

edited Nov 22, 2013 at 7:45

answered Nov 22, 2013 at 7:02

Suresh Atta

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Comments

Rahul · Accepted Answer · 2013-11-22 07:02:44Z

4

Declare them as instance variables and initialize them in the Constructor. If you declare and initialize them in the constructor, they'll will be accessible only within the constructor(local scope) and wouldn't be accessible elsewhere, thus rendering them, useless.

private String word;
private String blanks;

public Hangman () {
    word = "p u m p k i n";
    blanks = "_ _ _ _ _ _ _";
}

// Have setters and getters for word and blanks if possible.

answered Nov 22, 2013 at 7:02

Rahul

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Comments

SimplyPanda · Accepted Answer · 2013-11-22 07:04:01Z

2

Because you declare word in the constructor, ie the text:

String word = "p u m p k i n";
String blanks = "_ _ _ _ _ _ _";

is within the brackets of public Hangman(), it is local to the constructor. It only exists in the scope of the constructor.

To fix this, bring the declaration of the variables outside like so:

public class Hangman{

private String word;      //declaring class variables as private
private String blanks;    //is a common best-practice

public Hangman () {
    word = "p u m p k i n";
    blanks = "_ _ _ _ _ _ _";
}

int k = word.length(); ... rest code after this

As for why we like to declare class variables as private, the Wikipedia article on encapsulation may be useful.

answered Nov 22, 2013 at 7:04

SimplyPanda

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Comments

Aniket Thakur · Accepted Answer · 2013-11-22 07:02:39Z

1

You have to do the following

public class Hangman{

private String word;
private String blanks

public Hangman () {

    word = "p u m p k i n";
    blanks = "_ _ _ _ _ _ _";


}
 int k = word.length(); ... rest code after this

So basically you have to define your variables as instance variables rather than local variables(which you have done). If you want to access it in your class later it's scope should be such which is why you must make it instance variables. Also for the record instance variables are assigned default values.

answered Nov 22, 2013 at 7:02

Aniket Thakur

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