Added stack

stack.java

@@ -0,0 +1,87 @@
+A stack is an Abstract Data Type (ADT), commonly used in most programming languages. It is named stack as it behaves like a real-world stack, for example – a deck of cards or a pile of plates, etc.
+
+Stack operations may involve initializing the stack, using it and then de-initializing it. Apart from these basic stuffs, a stack is used for the following two primary operations −
+
+
+
+ 1)push() − Pushing (storing) an element on the stack.
+
+  A simple algorithm for Push operation can be derived as follows −
+
+begin procedure push: stack, data
+
+   if stack is full
+      return null
+   endif
+
+   top ← top + 1
+   stack[top] ← data
+
+end procedure
+
+
+
+
+ 2)pop() − Removing (accessing) an element from the stack.
+A simple algorithm for Pop operation can be derived as follows −
+
+begin procedure pop: stack
+
+   if stack is empty
+      return null
+   endif
+
+   data ← stack[top]
+   top ← top - 1
+   return data
+
+end procedure
+
+
+
+When data is PUSHed onto stack.
+
+To use a stack efficiently, we need to check the status of stack as well. For the same purpose, the following functionality is added to stacks −
+
+
+
+
+ 3)peek() − get the top data element of the stack, without removing it.
+
+ Algorithm of peek() function −
+
+begin procedure peek
+   return stack[top]
+end procedure
+
+
+
+ 4)isFull() − check if stack is full.
+
+  Algorithm of isfull() function −
+
+begin procedure isfull
+
+   if top equals to MAXSIZE
+      return true
+   else
+      return false
+   endif
+
+end procedure
+
+
+
+ 5)isEmpty() − check if stack is empty.
+
+  Algorithm of isempty() function −
+
+begin procedure isempty
+
+   if top less than 1
+      return true
+   else
+      return false
+   endif
+
+end procedure