Java Class : How do I set up a toString method for arrays?

I'm having a problem with the toString method, or my code could be wrong. Heres an example:

Code :

---

 public class TestClass
{
  private TestClass[] a;
  private int[] b;
 
  public TestClass(int...b) // Constructor
  {
   this.b
  {
   public TestClass[] concat(TestClass...b1)
  {
     TestClass[] temp = new TestClass[b1.length+b.length]
     for(int i = 0;i<=temp.length;i++)
      return TestClass(temp[i]);  //Trying to return the elements of two arrays put together, I think this could be wrong
}

---

How would I do my toString?
I want to be able to do something like this :
(main)

Code :

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TestClass a1 = new TestClass[1,2,3,4];
TestClass a2 = new TestClass[5,6,7,8,9];
TestClass a3;  // Need help on this also, how do I overload my constructor to get an empty set of array?
a3 = a1.concat(a2);
System.out.print(a3); //Want the results " 1,2,3,4,5,6,7,8,9,10 "

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I'll walk you through a simple example of how to override the toString() method:

Let's say we have class named A, which had an int variable var which was set in the constructor:

Code java:

---

public class A {
     int var = 0;
 
     public A(int n) {
          var = n;
     }
}

---

Now let's say we want to override A's toString() method to print the value of var 5 times. Our new class would look like:

Code java:

---

public class A {
     int var = 0;
 
     public A(int n) {
          var = n;
     }
     public String toString() {
          String ret = var+"";
          ret = ret+var;
          ret = ret+var;
          ret = ret+var;
          ret = ret+var;
          return ret;
     }
}

---

Now, if we create a main that creates an A Object, and prints out an A Object to the console, our main would look like this:

Code java:

---

public class someClass {
     public static void main(String[] args) {
          A aObj = new A(5);
          System.out.println(aObj);
     }
}

---

and our output would look this like:

Quote:

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55555

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Now, that is how to override a toString() method. But what about printing out an array? Well, we can call a println on an array. Let's say we had a main which had an int array with the numbers 1 through 5. Then let's print out the array, both by just calling it, and with each int on its own line:

Code java:

---

public class someClass {
     public static void main(String[] args) {
          int[] array = new int[]{1,2,3,4,5};
          System.out.println(array);
          for(int i=0;i<array.length;i++)
               System.out.println(array[i]);
     }
}

---

And our output would be:

Quote:

---

[1, 2, 3, 4, 5]
1
2
3
4
5

---

With all of that information (and your knowledge of looping through an array which I see you have), see if you can figure some of it out. If you have some trouble, feel free to ask.

Quote:

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a3 = a1.concat(a2)

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For that to work, concat() needs to return a TestClass object.

@ aussiemcgr, much thanks, understand the toString now.

@Norm
I just notice examples in my book about that.

So now I have a little problem understanding the constructor. How would I set it up?

Code :

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private int[] aList = new int[200]; //instance v
 
public TestClass(int[] a) // constructor
{
	aList = a;
}

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Would this allow to to create an object that takes in a list of array .
ex. :

Code :

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TestClass t = new TestClass(1,2,3,4,5);

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First time making a class while dealing with arrays, so I'm kind of loss.

Have you coded the class and compiled it? What happened?
Have you tried the code in post#1?

Wont let me compile :

Code :

---

  public TestClass[] concat(TestClass...b1)
  {
     TestClass[] temp = new TestClass[b1.length+b.length]
     for(int i = 0;i<=temp.length;i++)
      return TestClass(temp);

---

Wont let me grab the length of b1, so i figured something is wrong with my constructor.

Please post the full text of the compiler's error message.

"Exception in thread "main" java.lang.Error: Unresolved compilation problem:
length cannot be resolved or is not a field

at TestClass.concat(TestClass.java:41)
at TestClassDriver.main(TestClassDriver.java:8)"



at TestClass.concat(TestClass.java:41) is :

Code :

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TestClass[] temp = new TestClass[b1.length+b.length]

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at TestClassDriver.main(TestClassDriver.java:8) is :

Code :

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a3 = a1.concat(a2)

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What you posted is an execution time error, not a compiler error. There is no stack trace for compiler errors.

Can you post the full text of the compiler error message? The error messages I get include the source line and a ^ under where the error is located:

Code :

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TestSorts.java:138: cannot find symbol
symbol  : variable var
location: class TestSorts
         var = 2;
         ^

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Hmm. Using eclipse, and on the line with the x it just says : "length cannot be resolved or is not a field"

Sorry, you need to use the javac compiler to get good compiler error messages. The error messages I get compiling your code have nothing to do with the length attribute.