Merge pull request #170 from AayushBangroo/master

Generic Stack class added

Author: SarthakKeshari

Data Structure/Stack/GenericStack.java

@@ -0,0 +1,126 @@
+/*
+Statement: Implement a Generic Stack class in Java
+ */
+
+import java.util.ArrayList;
+
+class Stack<T> {
+    private final ArrayList<T> stack;
+    private final int size;
+    private int top;
+
+    //initialize stack and its fields
+    public Stack(int size) {
+        this.size = size;
+        this.top = -1;
+        stack = new ArrayList<>(size);
+    }
+
+    //Returns top value in stack
+    public T top() {
+        if (top == -1) {
+            System.out.println("Stack is empty");
+            return null;
+        }
+
+        return stack.get(top);
+    }
+
+    //Removes top value in stack and returns the popped value
+    public T pop() {
+        if (top == -1) {
+            System.out.println("Stack is empty");
+            return null;
+        }
+
+        T popped = stack.get(top);
+        //set value to null
+        stack.set(top, null);
+        top--;
+        return popped;
+    }
+
+    //Push value in stack
+    public void push(T val) {
+        //check if stack is full
+        if (top == size - 1) {
+            System.out.println("Stack overflow");
+            return;
+        }
+
+        //push new value in stack
+        stack.add(val);
+        top++;
+    }
+
+    //checks if stack is empty
+    public boolean isEmpty() {
+        return top == -1;
+    }
+
+    //get stack size
+    public int size() {
+        return this.size;
+    }
+
+    //print stack data and meta-data
+    @Override
+    public String toString() {
+        return "Stack{" +
+                "stack=" + stack +
+                ", size=" + size +
+                ", top=" + top +
+                '}';
+    }
+}
+
+public class GenericStack {
+    public static void main(String[] args) {
+        //stack of integers of size 10
+        Stack<Integer> integerStack = new Stack<>(10);
+
+        //fill the stack completely
+        for (int i = 0; i < integerStack.size(); i++) {
+            integerStack.push(i);
+        }
+
+        //print stack information
+        System.out.println(integerStack);
+
+        //print top value in stack
+        System.out.println(integerStack.top());
+
+        //stack is full
+        integerStack.push(100);
+
+        //pop all elements in stack
+        for (int i = 0; i < integerStack.size(); i++) {
+            integerStack.pop();
+        }
+
+        //print stack information
+        System.out.println(integerStack);
+
+        //stack underflow
+        integerStack.pop();
+
+        //stack of String of size 5
+        Stack<String>stringStack = new Stack<>(5);
+
+        stringStack.push("Hello");
+        stringStack.push("Java");
+        stringStack.push("Programmers");
+
+        //get top value in stack
+        System.out.println(stringStack.top());
+
+        //pop the stack and get popped value
+        String poppedValue = stringStack.pop();
+
+        //print popped value
+        System.out.println(poppedValue);
+
+        //print stack information
+        System.out.println(stringStack.toString());
+    }
+}