A stack is a collection of objects that follows the last-in-first-out(LIFO) principle. Elements can be inserted at any time, and only the last element inserted can be removed at any time. This word is a metaphor for a stack of spring-loaded plates in a cafeteria plate dispenser. The "pushing" and "popping" of plates into the stack are the basic procedures in this situation. We "pop" the top plates of the stack to make room for more plates when we need them, and we "push" plates we add down to take their place as the new top plate. A PEZ candy dispenser can be another metaphor. The dispenser that is spring-loaded stores mint candies "pops" out the top-most
candy in the sweets of candies in the container when the top of the dispenser lifts. Stacks are fundamental in Data Structures and are used in many applications.
Some of these applications are as follows: Web Browsers on the Internet actually store the addresses of the sites the user recently visited on a stack. When the user visits a new website, the site's address is then "pushed" onto the stack of the other addresses of sites of the user. The browser can allow users to "pop" back to the previously visited sites using the browser's back button. Another use is when text editors, which often have an "undo" option, cancel recent editing activities and return the document to its previous state.
Although Stacks are the simplest of all data structures, they are also amongst the most significant data structures due to their widespread use in various applications that also use numerous more complex data structures. A stack is an abstract data type that supports two methods: push (element e) and pop().
The method push(element e) inserts element e at the top of the stack while the method pop() removes the last element added and returns the top element on the stack. The error will occur when the stack is empty—additionally, defining the following methods size(), which returns the number of elements in the stack, and isEmpty() which returns a True/False statement(Boolean) indicating if the stack is empty, and top() which returns the top element in the stack without actually removing it. Error will occur when the stack is empty.
Since it is important, stack is included as a "built-in" class in the java.util package of Java. The class java.util.Stack stores elements and it includes the methods, push(), pop(), peek(); which is technically top(), size() and empty(); which is technically isEmpty(). The methods pop() and peek() throws an exception if they are called on an empty stack. Although it is more convinient to just use the class, it's still important to learn how to implement a stack from scractch. In Java, there are two steps to implementing a data type. The first step is to define a Java Application Programming Interface (API), also known as an interface, which outlines the names of the methods that the ADT supports as well as their intended usage. Additionally, we should know the exceptions for any error conditions. For an instance, the error condition when calling pop() or top() on an empty stack is called by throwing EmptyStackException.
By keeping a stack's components in an array, we can implement a stack. In this case, the stack is specifically an N-element array of integers that contains the index of the top element.
As they are essential to many programming tasks, stacks should be understood by every programmer. Knowing how to use stacks efficiently will unquestionably improve your problem-solving skills in Java programming, whether you're handling function calls, parsing expressions, or putting backtracking algorithms into practice.
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