Last update 8. January 2021.

A stack in Java is a collection (or group) of elements that are first saved in last order (LIFO). In other words, a stack is a data structure that stores the data first.

This means that the item last stored in the stack is the first item to be removed from the stack. Only the top cell of the stack is currently available.

When an element (object) is placed in the stack, this is called a push operation. We can make a pile of all kinds of elements.

When an item is removed from the stack, it is called a pop operation.

Finding an item in the stack is called an operation.

The insertion and removal of elements takes place only on one side of the stack, which is traditionally called the top of the stack. This means that new objects are added to the top of the stack and objects are removed from the top of the stack.

That is why the stack is called the final data structure. A typical example of a stack in Java can be seen in the following figure.

java stack

As you can see in the picture above, we have added three elements A, B and C to the stack. When they are removed from the stack, we get the fashion items C, B and A. This mode is called the last-in, first-out data structure. Let’s break down the examples in real time to understand them better.

Example of a real-time stack in Java

1. An example of a real-time stack is a stack of books, as shown in the following figure. You can’t take a book out of the pile without first putting away the books that are stacked.

Example of a real-time stack in Java

2. A second example of a real-time stack is the cafeteria plate stack, where the last washed plate is removed first before use.

3. In the same way, with DVD media, the CDs are arranged so that the last CD is released first and can be used. This is also an example of a pile.

The stack class was introduced in Java version 1.0. It is included in the java.util.Stack package. This class is now considered a legacy class in Java because it does not comply with the Java Collections Framework.

The Java API recommends using the Java ArrayDeque class instead of the stack. ArrayDeque offers all the usual functions of the stack and is JCF compliant.

Java Stack Class Hierarchy

The Java Stack class expands a vector class extending the AbstractList class. It implements the list interface and the RandomAccess interface. The Stack class also implements serializable and clonable interfaces. A hierarchical scheme of the stack in Java is shown in the following figure.

http://server.digimetriq.com/wp-content/uploads/2021/01/1610119209_847_Stack-in-Java-Methods-Example-Program.png

Chimney class declaration

The stack is a generic class in Java that has the following statement in general form.

the public class Stack
expands the vector

Here E stands for the type of elements the stack can contain.

ClassBattery characteristics

There are several functions of the stack in Java that are as follows:

1. A stack is a group of elements of which the last and first fragment is the most recent.

2. In the Java stack, all operations take place at the top of the stack.

3. When the button is pressed, the element is placed at the top of the battery.

4. The Pop operation consists of removing an item from the stack and returning it.

5. The class of the stack is synchronized. That means it’s stringy.

6. Zero elements are allowed in the stack.

7. Duplicates are allowed in the pile.

Stack Class Builder in Java

The Stack class offers only one manufacturer that looks like this:
1. Stack(): This constructor is used to create an empty stacking object. The general form for creating a stacked object is as follows:

Stack stack = new Stack();
For example :
Stack stack = new Stack(); // Only objects of the whole type will be saved.

Stacking methods in Java

In addition to the methods inherited from the vector class, the stack has five other methods of its own. They’re like this:

1. empty boolean() : This method is used to check whether the battery is empty or not. Returns true only if the stack does not contain any element (object). Otherwise you get a false yield.

2. E look(): This method is used to remove the top cell from the battery without removing it.

3. E pop() : The pop() method is used to drag (remove) and drop the element from the top of the stack.

4. E push(E obj) : This method pushes an object element to the top of the stack and returns that element (object).

5. int search(Object obj) : This method returns the position of the object element to the top of the stack. If the element is not present on the stack, -1 is returned.

Examples of programs in the Java Stack

Let’s take some examples of programs that perform different operations based on stack class methods in Java.

1. Add elements : We can use the push() method to add elements to the stack. The push() method places the element at the top of the stack.

Program source code 1 :

Import java.util.Stack ;
public class StackEx [
public static void main(String[] args)
[
// Create an empty stack of String objects.
Stack st = new Stack<>();

// checks whether the stack is empty or not.
empty boolean = st.empty() ;
System.out.println(Is stack empty : +empty) ;

// Adds elements to the top of the stack using the push() method.
st.push (Sunday);
st.push (Monday);
st.push (Tuesday);
st.push (Wednesday);
st.push (Thursday);
st.push (Friday);
st.push (Saturday) ;

// Display the stacks.
System.out.println(stack elements: +st);
}
}

Get out of here:
Empty battery:
real battery cells: (Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday)

2. Access element : Using the peek() method, we can extract or retrieve the element at the top of the stack without removing it. We will also time the position of the element in the stack using the search method(). Take a look at the source code below.

Program source code 2 :

Import java.util.Stack ;
public class StackEx2 [
public static void main(String[] args)
[
// Create an empty stack with Integer type objects.
Stack st = new Stack<>();

st.push(25);
st.push(30);
st.push(35);
st.push(40);
st.push(45);
st.push(50) ;

// Display the stacks.
System.out.println(stack elements: +st) ;

// Extraction element at the top of the stack.
Object peekElement = st.peek() ;
System.out.println(Item at the top of the stack : +peekElement) ;

// Get the position of the element in the stack.
System.out.println(position of element 50: +st.search(50));
System.out.println(position of element 80: +st.search(80));
}
}

Get out of here:
Stacking elements : 25, 30, 35, 40, 45, 50] Point
at the top of the stack: 50
Position of point 50 : 1
Element position 80 : -1

3. Delete Items : In Java we can use the pop() method to remove an element from the stack.

Program source code 3 :

Import java.util.Stack ;
public class StackEx3 [
public static void main(String[] args)
[
// Create an empty stack with Integer type objects.
Stack st = new Stack<>();

st.push(25);
st.push(30);
st.push(35);
st.push(40);
st.push(45);
st.push(50) ;

// Display the stacks.
System.out.println(stack elements: +st) ;

// Remove elements from the stack, one by one.while(st.size() > 0){System.out.println(Removed element: +st.pop());}System.out.println(Empty stack: +st.empty());}}}.

Get out of here:
Stacking elements : 25, 30, 35, 40, 45, 50]Point deleted: 50point deleted: 45point deleted: 40point deleted: 35point deleted : 30 Point
deleted: 25
Battery empty: true.

Program source code 4 :

Import java.util.Stack ;
public class StackEx4 [
public statically void head(String[] args)
[
Stack st = new Stack<>() ;

st.push(25);
st.push(30);
st.push(35);
st.push(40);
st.push(45) ;

System.out.println(original stacked elements: +st);
System.out.println(pop-element: +st.pop());
System.out.println(original stacked elements: +st.println(stacked elements after removal: +st);
System.out.println(push element: +st.push(50));
System.out.println(stacked elements after addition: +st);
}
}.

Get out of here:
Original stacking elements : 25, 30, 35, 40, 45] Pop element : 45
Stackable elements after removal : 25, 30, 35, 40] Sliding element : 50
Stacking elements after addition : [25, 30, 35, 40, 50]

Explanation:

Push and Pop operations in the Java Stack
Refer to the figure above to better understand the Push and Pop operations in the Java Stack.

I hope that this lesson has covered the important points related to the stackklas in Java with real-time examples and programs with graphs. I hope you understand that.
Thanks for reading!

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