A) Write a generic Java queue class (a plain queue, not a priority queue). Then, call it GenericQueue, because the JDK already has an interface called Queue. This class must be able to create a queue of objects of any reference type. Consider the GenericStack class shown below for some hints. Like the Stack class below, the GenericQueue should use an underlying ArrayList<E>. Write these methods and any others you find useful:enqueue() adds an E to the queuepeek() returns a reference to the object that has been in the queue the longest, without removing it from the queuedequeue() returns the E that has been in the queue the longest, and removes it from the queuecontains(T t) returns true if the queue contains at least one object that is equal to t *in the sense that calling .equals() on the object with t the parameter returns true.* Otherwise contains returns false. size() and isEmpty() are obvious. ```javapackage stackdemo;// http://cs.fit.edu/~ryan/java/programs/generic/GenericStack-java.htmlimport java.util.*;public class GenericStack { private ArrayList stack = new ArrayList(); private int top = 0; // the list index where the next T added to the stack will be public int size() { return top; } public void push(T item) { // this method takes a T as an argument stack.add(top++, item); } public T pop() { // this method returns a T return stack.remove(--top); }}```### Code Explanation:- **Package Declaration:** - `package stackdemo;` indicates that this class is part of the `stackdemo` package. - **Import Statement:** - `import java.util.*;` imports all utility classes from the `java.util` package, including `ArrayList`.- **Class Definition:** - `public class GenericStack` declares a generic class `GenericStack` with a type parameter `T`.- **Class Members:** - `private ArrayList stack`: A private list to hold the stack elements of type `T`. - `private int top`: An integer representing the index for the next element to be added to the stack.- **Methods:** - `public int size()`: Returns the current size of the stack, represented by `top`. - `public void push(T item)`: Adds an item to the stack and increments the `top` index. - `public T pop()`: Removes and returns the top element on the stack, decrementing the `top` index.

1. **Initialization:**Create a class named `GenericQueue` with a type parameter `E` for generic…

Answered: A) Write a generic Java queue class (a…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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A) Write a generic Java queue class (a plain queue, not a priority queue). Then, call it GenericQueue, because the JDK already has an interface called Queue. This class must be able to create a queue of objects of any reference type. Consider the GenericStack class shown below for some hints. Like the Stack class below, the GenericQueue should use an underlying ArrayList<E>.

Write these methods and any others you find useful:

enqueue() adds an E to the queue

peek() returns a reference to the object that has been in the queue the longest, without removing it from the queue

dequeue() returns the E that has been in the queue the longest, and removes it from the queue

contains(T t) returns true if the queue contains at least one object that is equal to t *in the sense that calling .equals() on the object with t the parameter returns true.* Otherwise contains returns false.

size() and isEmpty() are obvious.

```java
package stackdemo;
// http://cs.fit.edu/~ryan/java/programs/generic/GenericStack-java.html
import java.util.*;

public class GenericStack<T> {
private ArrayList<T> stack = new ArrayList<T>();
private int top = 0; // the list index where the next T added to the stack will be

public int size() {
return top;
}

public void push(T item) { // this method takes a T as an argument
stack.add(top++, item);
}

public T pop() { // this method returns a T
return stack.remove(--top);
}
}
```

### Code Explanation:

- **Package Declaration:**
- `package stackdemo;` indicates that this class is part of the `stackdemo` package.

- **Import Statement:**
- `import java.util.*;` imports all utility classes from the `java.util` package, including `ArrayList`.

- **Class Definition:**
- `public class GenericStack<T>` declares a generic class `GenericStack` with a type parameter `T`.

- **Class Members:**
- `private ArrayList<T> stack`: A private list to hold the stack elements of type `T`.
- `private int top`: An integer representing the index for the next element to be added to the stack.

- **Methods:**
- `public int size()`: Returns the current size of the stack, represented by `top`.
- `public void push(T item)`: Adds an item to the stack and increments the `top` index.
- `public T pop()`: Removes and returns the top element on the stack, decrementing the `top` index.

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