Question:
I have few problems with the following code:

 abstract class AbstractGraph extends java.awt.Frame {   static int HighValue,LowValue,ArraySize;   static String InstancesArray[][] = new String [20][ArraySize];    float ReturnArray(String name)   {     …   }  static void AddArray(String name,float array[])   {     …   }  }

The InstancesArray holds a name and values of arrays created by a given user.

My first problem is that I could not access the variable ArraySize from a different class. I had to make it static first; only then was I able to assign a value to it from other function.

But then the array created did not have these dimensions; instead, it gave me exceptions when I tried to input something into the array.

I also can’t for some reason return an array from the ReturnArray method.

Also, I don’t understand why I had to make the method AddArray static to be able to do what it is supposed to do (add name and values of arrays created by a user to the InstancesArray).

Answer:
If I understand your application, you want to maintain an array ofbindings between names (represented as Strings) and associated arrays offloating point numbers.

If I’m correct, your initial declaration of instanceArray:

 String instancesArray[] …

is not correct, because it declares a two-dimensional array of Strings.

Instead, instancesArray should be declared as an array of Bindings:

 private Binding instancesArray[];

A Binding object holds a String and an associated array of floats. It alsoprovides some useful constructors. For example:

class Binding {   public String name;   public float[] values;   public Binding() {      name = new String(“void”);      values = new float[0];   }   public Binding(String s) {      name = s;      values = new float[0];   }   public Binding(String s, float[] nums) {      name = s;      values = nums;   }}

In this case, here’s what your returnArray method might look like:

public float[] returnArray(String name) {      for(int i = 0; i < graphSize; i++)         if (instanceArray[i].name.equals(name))            return instanceArray[i].bindings;      return new float[0];   }

Your next problem seems to be lack of a constructor. Of course you won’tbe able to instantiate your AbstractGraph class as long as it’s declaredabstract (I assume you had good reason to do this), so your constructorwill appear in a derived class.

To simplify things, I declared Graph as a concrete class. Myconstructor allows users to specify the length of instancesGraph:

class Graph {   private int arraySize, graphSize   private Binding instancesArray[];   public Graph(int gs) {      graphSize = gs;      instancesArray = new Binding[gs];      for(int i = 0; i < 20; i++)          instancesArray[i] = new Binding();   }   public float[] returnArray(String name) {...}   public void addArray(String name, float[] array) {...}}

My addArray is pretty kludgy. It looks for the next available space ininstancesArray and modifies the binding there. You can probably think of100 better ways to do this:

public void addArray(String name, float[] array) {      int next = -1;      for(int i = 0; i < graphSize; i++)          if (instanceArray[i].name.equals("null")) {            next = i;            break;         }      if (next > -1) {         instanceArray.name = name;         instanceArray.values = array;      }   }}

Finally, main() constructs a graph g, and starts adding bindings to it:

public Main {   public static void main() {      Graph g = new Graph(20);      float[] vals = new float[3] = {100, 200, 300};      g.addBinding(“first”, vals);      …   }}

Without declaring and initializing instances of the Graph class, only thegraph class itself exists as an object. The only members of a class objectare those declared static.