Checking in Queue implementation of Array

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+  </component>
+</project>

clients/src/main/java/com/hithomelabs/clients/ArrayQueueClient.java

@@ -0,0 +1,22 @@
+package com.hithomelabs.clients;
+
+import com.hithomelabs.princeton1.module4.ArrayQueue;
+import com.hithomelabs.princeton1.module4.ArrayStack;
+import com.hithomelabs.princeton1.module4.Queue;
+import com.hithomelabs.princeton1.module4.Stack;
+
+public class ArrayQueueClient {
+    public static void main(String[] args) {
+        Queue<Integer> queue = new ArrayQueue<Integer>();
+        for(int i = 0; i < 21; i++){
+            queue.enqueue(i);
+        }
+        for(int i = 0; i < 13; i++){
+            System.out.println(queue.dequeue());
+        }
+
+        // Using object s, as stack is generic but every java Object has implementation of toString()
+        for (Object s : queue)
+            System.out.println(s);
+        }
+    }

module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayQueue.java

@@ -0,0 +1,103 @@
+package com.hithomelabs.princeton1.module4;
+
+import javax.annotation.Nonnull;
+import java.util.Iterator;
+
+public class ArrayQueue<E> extends Queue<E>{
+
+    // insertion from tail, removal from head
+    public static final int DEFAULT_CAPACITY = 10;
+    private int capacity;
+    private int tail;
+    private int head;
+    private int size;
+    private E[] arr;
+
+    public ArrayQueue(){
+        this(DEFAULT_CAPACITY);
+    }
+
+    public ArrayQueue(int capacity){
+        this.capacity = capacity;
+        arr = (E[]) new Object[this.capacity];
+        size = 0;
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return size == 0;
+    }
+
+    @Override
+    public E dequeue() {
+        if(isEmpty())
+            return null;
+        else{
+            E element = arr[head];
+            // Garbage collection
+            arr[head] = null;
+            head = (head+1)%capacity;
+            size = size - 1;
+            if(capacity >= 40 && size < capacity/4){
+                capacity = capacity/2;
+                resize(capacity, capacity*2);
+            }
+            return element;
+        }
+    }
+
+    @Override
+    public void enqueue(E element) {
+        // We plan capacity expansion if needed
+        if (size == capacity){
+            capacity = capacity * 2;
+            resize(capacity, capacity/2);
+        }
+        arr[tail] = element;
+        tail = (tail + 1) % capacity;
+        ++size;
+    }
+
+    // When resize takes place always the original array is full, so copy the complete array as is
+    private void resize(int capacity, int oldCapacity) {
+        E[] resizedArr = (E[]) new Object[capacity];
+        for(int i = 0; i < size; i++) {
+            resizedArr[i] = arr[head];
+            // halving because capacity has now doubled
+            arr[head] = null;
+            head = (head + 1) % oldCapacity;
+        }
+        arr = resizedArr;
+        // When resizing takes place, we bring the head to 0 and the tail to size
+        // tail is where new inserts will be made and head will be where elements will be removed
+        tail = size;
+        head = 0;
+
+    }
+
+    @Override
+    public int size() {
+        return size;
+    }
+
+    @Override
+    @Nonnull
+    public Iterator<E> iterator() {
+        return new Iterator<E>() {
+            int counter = size;
+            int pointer = head;
+            @Override
+            public boolean hasNext() {
+                return counter != 0;
+            }
+
+            @Override
+            public E next() {
+                E element = arr[pointer];
+                pointer = (pointer + 1)% capacity;
+                --counter;
+                return element;
+            }
+        };
+    }
+}

module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayStack.java

@@ -1,4 +1,5 @@
 package com.hithomelabs.princeton1.module4;
+import javax.annotation.Nonnull;
 import java.util.Iterator;
 
 // Concrete implementation of stack using arrays
@@ -14,7 +15,7 @@ public class ArrayStack<E> extends Stack<E> {
 
     public ArrayStack(int capacity){
         this.capacity = capacity;
-        this.arr = (E[]) new Object[this.capacity];
+        arr = (E[]) new Object[this.capacity];
     }
 
     // Constructor chaining, default constructor will call parametrised constructor with default initial capacity 10
@@ -24,20 +25,20 @@ public class ArrayStack<E> extends Stack<E> {
 
     @Override
     public boolean isEmpty() {
-        return this.size == 0;
+        return size == 0;
     }
 
     private void changeCapacity(int newCapacity){
         E[] resizedArr = (E[]) new Object[newCapacity];
-        for (int i = 0; i < this.size; i++)
-            resizedArr[i] = this.arr[i];
-        this.arr = resizedArr;
+        for (int i = 0; i < size; i++)
+            resizedArr[i] = arr[i];
+        arr = resizedArr;
     }
 
     private void incrementSize(){
-        if (this.size == this.capacity){
-            this.capacity = 2 * this.capacity;
-            changeCapacity(this.capacity);
+        if (size == capacity){
+            capacity = 2 * capacity;
+            changeCapacity(capacity);
         }
     }
 
@@ -46,8 +47,8 @@ public class ArrayStack<E> extends Stack<E> {
     @Override
     public void push(E element) {
         // Lazy approach, we assume size to always be lesser than capacity
-        this.incrementSize();
-        this.arr[this.size++] = element;
+        incrementSize();
+        arr[size++] = element;
     }
 
     @Override
@@ -55,26 +56,27 @@ public class ArrayStack<E> extends Stack<E> {
         if (isEmpty())
             return null;
         else{
-            E e = this.arr[--this.size];
-            this.arr[this.size] = null;
-            this.checkResize();
+            E e = arr[--size];
+            arr[size] = null;
+            checkResize();
             return e;
         }
     }
 
     private void checkResize() {
-        if (this.size < this.capacity / 4 && this.capacity > 10){
-            this.capacity = this.capacity / 2;
-            changeCapacity(this.capacity);
+        if (size < capacity / 4 && capacity >= 40){
+            capacity = capacity / 2;
+            changeCapacity(capacity);
         }
     }
 
     @Override
     public int size() {
-        return this.size;
+        return size;
     }
 
     @Override
+    @Nonnull
     public Iterator<E> iterator() {
         return new Iterator<E>() {
 

module4/src/main/java/com/hithomelabs/princeton1/module4/Queue.java

@@ -0,0 +1,10 @@
+package com.hithomelabs.princeton1.module4;
+
+public abstract class Queue<E> implements Iterable<E> {
+
+    public abstract boolean isEmpty();
+    public abstract E dequeue();
+    public abstract void enqueue(E element);
+    public abstract int size();
+}
+