How To Implement Stack Inwards Coffee Using Array Together With Generics - Example

The stack is 1 of the pop information construction which supports LIFO (Last In First OUT) operation. Due to LIFO advantage, y'all tin purpose stack information construction to convert a recursive algorithm to an iterative one. Stack data construction is really tardily to implement using an array or linked list, but y'all don't receive got to implement it past times your ain because Java already provides a Stack implementation in java.util.Stack class. This flat is a subclass of the Vector flat together with y'all should purpose it whenever y'all demand Stack for your production code, in that place is no quest inventing the bicycle 1 time to a greater extent than when the focus is on developing your application. At the same time, equally a programmer together with coder, y'all should also know how to implement your ain stack past times using a basic information construction similar an array or linked list.

It's really of import for a programmer to larn how to implement diverse information construction inwards his favorite programming linguistic communication e.g. binary search tree, linked list, Stack, or Queue. They are also pop coding interview query together with y'all may run across them when y'all to your adjacent labor interview.

Here nosotros are implementing Stack inwards Java exclusively from a coding interview perspective, if y'all ever demand to purpose a Stack inwards your real-world Java application y'all should purpose the 1 from java.util parcel or from some 3rd political party library e.g. GS collection, FastUtil or Trove. They render the high-performance implementation of diverse collection classes inwards Java.

How to implement Stack inwards Java using array

Stack has next interface together with supports operations similar push(), pop(), contains(), clear() together with size(). The pop() method volition ever render the finally chemical constituent added.

Since Java provides Generics to ensure type-safety, it's recommended to purpose Generics whenever y'all write a container flat i.e. a flat which holds objects of other classes e.g. this Stack flat which tin concur whatsoever type of object similar String or Integer etc. While using this flat y'all precisely demand to country the flat that which sort of object volition hold upward stored together with the compiler volition ensure that no other type of object volition hold upward stored inwards this stack.

I receive got used Generics hither to present how y'all tin write type-safe classes inwards Java, but if y'all demand a refresher y'all tin read this article earlier trying the code instance given inwards this article.

Now, let's come upward to the crux of this example, the logic y'all demand to build or so array to implement diverse Stack operations e.g. push, pop, contains, size, isEmpty, together with clear. Since nosotros are using array information construction to implement Stack, nosotros volition purpose an array to shop all elements. Since the size of the array needs to hold upward declared at the fourth dimension of creating the array, we'll purpose a default capacity of 10. The user tin also do Stack of whatsoever capacity past times providing value inwards the constructor.


One of the key departure betwixt array together with Stack, the sometime is a static information construction where size cannot hold upward changed 1 time declared but Stack is a dynamic information structure, it tin resize itself, but nosotros are non implementing the same resize logic hither to cash inwards one's chips on the computer programme simple. You tin banking firm correspond the code of Stack.java to reckon how it resize itself. It uses ensureCapacity() method to do a novel array amongst 1.5 capacity when threshold is breached, similar to the load factor of HashMap. After creating a novel array, it precisely copies content from the old array to novel array.

Coming dorsum to the implementation of Stack, the size(), clear() together with isEmpty() implementation is forthwith forward. We cash inwards one's chips on a variable size, which is incremented when an chemical constituent is added i.e. pushed into Stack together with decrement it when an chemical constituent is removed i.e. popped from Stack. The value of size variable is returned past times the size() method together with it shows how many elements are acquaint inwards Stack.

Many programmers brand a error hither past times returning the length of the array, which is wrong because the length of the array is genuinely the capacity of Stack. The stack could hold upward total or empty. So don't render the length of the array from size() method. Similarly, the isEmpty() method volition render true if size is zero.

The implementation of the clear() method is a footling flake tricky, some programmer brand the container array equally zip but clear is supposed to clearn the Stack, so that nosotros tin reuse the same array. So instead of precisely declaring array = null, y'all should iterate over the array until the size together with score every chemical constituent equally null. You don't demand to iterate the array until length, precisely iterating until the size is plenty because residue of the elements are already null.

Now, let's implement 2 of the most of import operations from the array, the push() together with pop() operation. The commencement thing, push() method does is it checks if Stack is total or not. If Stack is total i.e. size == length together with then it resizes the stack past times creating some other array of 1.5 times of master copy size together with copying the content of old array into a novel array. I receive got used Arrays.copyOf() method to trim back the size of the array. This method copies the specified array, truncating or padding amongst nulls (if necessary) so the re-create has the specified length.

If nosotros receive got space, together with then nosotros precisely shop the chemical constituent inwards the electrical current index together with increases the size. It's worth checking the clever purpose of the postfix ++ operator here, which commencement shop the chemical constituent at electrical current slot together with and then increment the value. So, at the start, size is 0 thence the commencement chemical constituent volition hold upward stored at 0th index inwards array together with size volition cash inwards one's chips 1.

On the other hand, the pop() functioning commencement checks if the array is empty, if it is empty together with then it render null, otherwise it commencement reduces the size together with and then render the value from the top of the stack i.e. electrical current index. Instead of using postfix operator, hither I receive got used prefix -- operator because size is ever 1 to a greater extent than than the electrical current index of the array. For example, if in that place is 1 chemical constituent inwards the array together with then size is 1 but the index of the chemical constituent is 0, thence nosotros commencement trim back the size together with and then retrieve the value from the array.

One of the key things y'all should hold upward aware hither is of retentivity leak caused past times keeping a reference of already popped out elements inwards Stack equally shown inwards Effective Java. To foreclose that nosotros are assigning zip to the electrical current slot inwards the array e.g. array[size] == null. This volition ensure that array is non keeping whatsoever reference to the object together with if that is exclusively referenced together with then object is at nowadays eligible for garbage collection.

One to a greater extent than affair y'all tin do inwards the pop() method is to trim back the size of the array if it's likewise big. We trim back the size of the array if it is larger than the capacity but cash inwards one's chips on it 1.5 times of size to render plenty headroom for growth.

Finally, y'all tin implement the contains() method past times doing a linear search inwards Java. This method should render truthful if an chemical constituent passed to this method exists inwards the Stack otherwise false. It but iterates through the array using enhanced for loop together with compares each chemical constituent of Stack to the given object, if they equal using equals() method together with then it returns true.

Java Program to implement Generic Stack using Array

Here is 1 instance of implementing Stack using an array inwards Java. In our example, nosotros receive got iii classes, first, the interface IStack to define functioning supported past times Stack implementation, minute the ArrayStack which implements this interface together with back upward all functioning past times storing elements inwards array, together with third, the StackDemo class, which is our essay flat to demonstrate how y'all tin purpose this Stack flat inwards your Java program.

You tin salvage these classes inwards split upward files e.g. IStack.java, ArrayStack.java, and StackDemo.java or y'all tin combine them inwards 1 flat equally I receive got done. Just recollect that when y'all shop them inwards split upward files, the mention of the file must hold upward same equally the mention of Blue Planet class.

StackDemo.java

import java.util.Arrays;  /**  * Java computer programme to essay our Stack implementation. In this computer programme  * nosotros add together distich of elements together with and then impress the Stack.  *  * @author Javin Paul  */ public class StackDemo {      public static void main(String[] args) {         IStack<Integer> stackOfInteger = new ArrayStack<>();         stackOfInteger.push(10);         stackOfInteger.push(20);          System.out.println("Stack of Integers : " + stackOfInteger);     } }

beck.java

/**  * An interface to stand upward for Stack information structure. We demand to mention it to  * something other than Stack because in that place is already a flat named Stack inwards  * java.util package.  *   * @author WINDOWS 8  *  * @param <T>  */ interface IStack<T> {     public boolean push(T value);      public T pop();      public boolean contains(T value);      public int size();      public void clear();      public boolean isEmpty();  }

ArrayStack.java

/**  * An implementation of Stack inwards Java using array. This flat is generic,  * so y'all tin do Stack of Integer or Stack of String.  *   * @author WINDOWS 8  *  * @param <T>  */ class ArrayStack<T> implements IStack<T> {      private static concluding int DEFAULT_CAPACITY = 10;     private T[] store;     private int size = 0;     private int capacity;      @SuppressWarnings("unchecked")     public ArrayStack() {         this.capacity = DEFAULT_CAPACITY;         shop = (T[]) new Object[DEFAULT_CAPACITY];     }      @SuppressWarnings("unchecked")     public ArrayStack(int capacity) {         this.capacity = capacity;         shop = (T[]) new Object[capacity];     }      @Override     public boolean push(T value) {         if (this.size >= store.length) {             int newSize = size + (size >> 1);             shop = Arrays.copyOf(store, newSize);         }          // non exclusively shop value inwards Stack but also         // increases size of the array, a skillful use         // ++ operator which ensures that first         // y'all shop at electrical current index together with than         // increment size.          store[size++] = value;         return true;     }      @Override     public T pop() {         if (size <= 0) {             return null;         }          // 1 time to a greater extent than commencement nosotros are reducing size together with and then getting value         // from Stack, because size is ever 1 to a greater extent than array index         // because index starts at 0. So if y'all receive got precisely one         // chemical constituent inwards Stack, together with then valid index is null but size         // would hold upward one.         T value = store[--size];          // brand certain y'all dereference chemical constituent at top of the stack         // to foreclose retentivity leak inwards Java         store[size] = null;          // shrinking array if its likewise big         int reducedSize = size;         if (size >= capacity && size < (reducedSize + (reducedSize << 1))) {             System.arraycopy(store, 0, store, 0, size);         }         return value;     }      @Override     public boolean contains(T value) {         // banking firm correspond for an chemical constituent inwards array using         // sequential search algorithm         boolean flora = false;         for (int i = 0; i < size; i++) {             T chemical constituent = store[i];             if (element.equals(value)) {                 flora = true;             }         }          return found;     }      @Override     public int size() {         return size;     }      @Override     public void clear() {         // brand certain y'all liberate reference of all         // chemical constituent to avoid retentivity leak inwards Java         for (int i = 0; i < size; i++) {             store[i] = null;         }         size = 0;     }      @Override     public boolean isEmpty() {         return size == 0;     }      /**      * returns String sentiment of Stack, fist chemical constituent      * is the top of stack      */     @Override     public String toString() {         StringBuilder sb = new StringBuilder();         sb.append("[");         for (int i = size - 1; i >= 0; i--) {             sb.append(this.pop());              if (i > 0) {                 sb.append(",");             }         }         sb.append("]");          return sb.toString();     } }  Output: Stack of Integers : [20,10]

JUnit tests for testing Stack information construction inwards Java

Now, let's essay our Stack implementation past times writing some unit of measurement essay using JUnit. Well, I did write them earlier writing code, precisely because I follow essay driven evolution sometimes, but it's your choice. You are ever gratis to add together to a greater extent than unit of measurement tests to embrace to a greater extent than scenarios. If y'all are non familiar amongst essay driven evolution inwards Java, I advise reading Test Driven: TDD together with Acceptance TDD for Java developers, 1 of my favorite mass on this topic.

Let me know if y'all notice whatsoever põrnikas on this Stack implementation using an array.

import static org.junit.Assert.*;  import org.junit.Test;  public class StackTest {      @Test     public void size() {         IStack<Integer> myStack = new ArrayStack<Integer>();         assertTrue(myStack.size() == 0);          myStack.push(1);         assertEquals(1, myStack.size());     }      @Test     public void isEmpty() {         IStack<Integer> newStack = new ArrayStack<Integer>();         assertTrue(newStack.isEmpty());          newStack.push(2);         assertFalse(newStack.isEmpty());          newStack.pop();         assertTrue(newStack.isEmpty());     }      @Test     public void clear() {         IStack<Integer> aStack = new ArrayStack<Integer>();         assertTrue(aStack.isEmpty());          aStack.push(2);         assertFalse(aStack.isEmpty());          aStack.clear();         assertTrue(aStack.isEmpty());     }      @Test     public void pushAndPop() {         IStack<String> bStack = new ArrayStack<String>();         assertEquals(0, bStack.size());                  bStack.push("one");         assertEquals(1, bStack.size());         bStack.push("two");         assertEquals(2, bStack.size());                  assertEquals("two", bStack.pop());         assertEquals("one", bStack.pop());         assertEquals(0, bStack.size());     } }

That's all close how to implement Stack information construction inwards Java using Array. It's also a skillful instance to meliorate your coding science because implementing cardinal together with advanced information construction inwards Java is non a trivial exercise, they brand y'all intend together with also challenge your coding technique. You tin non exclusively larn close information construction together with algorithm but also prepare the coding feel which is the biggest forcefulness of a programmer. If y'all desire to larn to a greater extent than close Stack together with other information structure, I advise y'all reading Introduction to Algorithms past times Thomas H. Cormen. It contains a wealth of information close essential information structures, which y'all won't notice anywhere.

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Thanks for reading this article. If y'all similar this article together with then delight part amongst your friends together with colleagues. If y'all receive got whatsoever questions, feedback, or proposition together with then delight drib a comment together with I'll effort to reply it. 

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