How can I pass a value from one constructor to another constructor?

Question

I'm working with Java. I have a class with 2 constructors. The first constructor takes an int value as a parameter and sets an int variable as that value. The second constructor takes a string and prints it out. The idea is that when I call the first constructor from my main class, it sets an integer value. And when I call the second constructor in the main class, it takes the string representation of int variable of the first constructor and prints it out.

Here's how I made the constructors:

public class Test
{
   int val;

   public Test(int x)
   {
      val = x;
      return val; //I know this won't work. So I'm looking for an alternative
   }

   public Test(String y)
   {
      System.out.println("The value is " + y);
   }
}

And the main method (in a different class) looks like this:

public static void main(String [] args)
    {
        Test t1 = new Test(6);
        Test t2 = new Test(String.valueOf(t1)); //This won't work because the first constructor can't return a value
    }

So how exactly can I change the contents of the constructors so that I can pass val into the 2nd constructor?

`public Test(int x) { this(String.valueOf(x)); this.val = x; }` — ernest_k, Nov 13 '18 at 17:19
I don't think this is a duplicate -- the OP wants to create `t1`, and then use the value in a subsequent call. — KevinO, Nov 13 '18 at 17:20
`int six = 6; Test t1 = new Test(six); Test t2 = new Test(String.valueOf(six)); ` — Michael, Nov 13 '18 at 17:21
Not a dupe. The dupe is a symptom but there are *other* problems. — Makoto, Nov 13 '18 at 17:21
Possible duplicate of [How do I call one constructor from another in Java?](https://stackoverflow.com/questions/285177/how-do-i-call-one-constructor-from-another-in-java) — fantaghirocco, Nov 13 '18 at 17:28
@fantaghirocco: We've already established that this isn't a dupe of that. — Makoto, Nov 13 '18 at 17:36

score 2 · Answer 1 · answered Nov 13 '18 at 17:29

2

Override toString() to return value so when you so String.valueOf(t1) it will do the toString() method;

public class Test
{
   int val;

   public Test(int x)
   {
      val = x;  
   }

   public Test(String y)
   {
      System.out.println("The value is " + y);
   }

   @Override
   public String toString()
   {
      return String.valueOf(val);
   }
}

answered Nov 13 '18 at 17:29

locus2k

2,802
1
14
21

Didn't see this one, we said the same thing. – markspace Nov 13 '18 at 17:33

score 1 · Answer 2 · answered Nov 13 '18 at 17:31

I think what you are probably actually trying to do is to override the toString() method of Test.

public class Test
{
   int val;

   public Test(int x)
   {
      val = x;
   }

   @Override
   public String toString() {
       return "Test:"+val;
   }
}

Then you can do this:

public static void main(String [] args)
    {
        Test t1 = new Test(6);
        String s = t1.toString();
        // or this
        System.out.println( t1 ); // prints "Test: 6"
    }

score 0 · Answer 3 · answered Nov 13 '18 at 17:23

What you're describing is actually impossible without some changes.

First and foremost, t1 and t2 are two separate instances and the values inside of them have no bearing on one another. So t1 has x=6 and t2 has x=0 (because of default values).

If you want your second constructor to have a value of x that isn't 0, then you'll need to pass that in too.

public Test(int x, String s) {
    super(x);
    System.out.println(x);
}

score 0 · Answer 4 · answered Nov 13 '18 at 17:26

0

I think you don't really want two constructors. It seems like you're wanting to do something like the following:

public class Test
{
   int val;

   public Test(int x)
   {
      val = x;
   }

   public void printVal()
   {
      System.out.println("The value is " + val);
   }
   public static void main(String [] args)
   {
      Test t1 = new Test(6);
      t1.printVal();
   }
}

answered Nov 13 '18 at 17:26

Ryan Cogswell

75,046
9
218
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I would not use `printVal()`, but instead override the `toString()` method. In that case, you can do `System.out.println(t1.toString())` to print the value (including the message) to the screen. – MWB Nov 13 '18 at 17:32
Yes, I agree. Answer by @markspace is a better end result. I was trying to stay closer to the original code. – Ryan Cogswell Nov 13 '18 at 17:33

score 0 · Answer 5 · answered Nov 13 '18 at 17:31

Your requirement is kinda weird. But this will work even it is kinda weird

public class Test {
    private static int val;

    public Test(int x) {
        val = x;
    }

    public Test() {
        System.out.println("The value is " + String.valueOf(val));
    }

    public static void main(String[] args) {
        Test t1 = new Test(6);
        Test t2 = new Test();
    }
}

How can I pass a value from one constructor to another constructor?

5 Answers5