Stack and dynamic array implementation in Java -

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I need to implement a stack array using a dynamic array, which I had to make myself.

Here's my dynamic array: 

  Import java.util.Arrays; Public class array {public entity] dianare; Int counter = 0; Public Zero (int n) {dynArray = new int [n]; } Public zero doubleSize () {int currentSize = dynArray.length; Int newSize = currentSize * 2; DynArray = Arrays.copyOf (dynArray, newSize); } Private zero half size () {int currentSize = dynArray.length; Int newSize = currentSize / 2; DynArray = Arrays.copyOf (dynArray, newSize); } Public Zero Addition (int x) {dynArray [Counter] = x; Counter ++; Float ratio = (float) counter / (float) diamond line; If (ratio == 1) {doubleSize (); }} Public int rem () {int last = dynAray [counter 1]; DynArray [Counter-1] = 0; Counter--; Float ratio = (float) counter / (float) diamond line; If (ratio & lt; = 0.25) {halfSize (); } Previous return; } Public int (int i) {if (! (((I))) {//System.out.print ("can not be added"); Return i; } And instead dynArray [i]; } Enter the public zero (int x, int y) {float ratio = (float) counter / (float) dynArray.length; If (ratio == 1) {doubleSize (); } If (check (y)) {System.out.println ("Any such index, nothing is added" + y); } And {dynArray [y] = x; }} Public full lane () {return dynArray.length; } Public Boolean check (int index) {if (index

Here is my stack code: 

  public class stack {Private static array A; Generate Public Zero () {a = New Array (); } Zero push (int x) {a.add (x); }} Pop () {return a.rem (); } Boolean is empty () {return a.len () == 0; } Public static zero main (string [] args) {stack stack = new stack (;); Stack.create (); Stack.push (1); / * Int k = 1; Stack.push (2 * t); Stack.push (2 * k + 1); Stack.push (2 * k + 2); {System.out.println (stack.pop ()) for (Int i = 0; I & lt; 40; i ++); } When I type  stack.java  in  stack.push (1)  main, then it will send me

Code> NullPointerException on the line where it says a.add (x) . I do not understand why this is an exception.

Creates an example of its stack a new array , But does not call to create the array method, so dynArray remains redundant, and you receive NullPointerException ( DynArray [counter] = x; ).

You should probably call create in the constructor of array (or create to eliminate the code and its code Should be moved to the constructor)


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