Question

Please help JAVA

1. Create the following in Stack.java:

   1. An array of ints set to size 10 to represent the Stack, an int variable for the index

   2. A constructor that sets the index to -1

   3. A method called isEmpty (returns a boolean) that has no parameters. This method returns true if the Stack is empty and false if the Stack is not empty.

true

4. A method called push(returns a Boolean) that takes an int as a parameter. This method pushes, or adds, the int to the stack if there is available space. Returns true if it got added successfully and false if wasn't able to be added to the stack

true

true

5. A method called pop that takes has no parameter and returns an int. This method removes the next int from the stack and returns it.

Stack s = new Stack(); s.push(10); s.push(20); s.push(30); System.out.println(s.pop()); System.out.println(s);

30

20, 10

6. A method called peek that has no parameter. This method returns the next int from the Stack without removing, or popping, it from the Stack

Stack s = new Stack(); S.push(10); s.push(20); s.push(30); System.out.println(s.peek()); System.out.println(s);

30

30, 20, 10

7. Override the toString() method to be able to print the values in the stack separated by a comma. You should NOT pop() any of the values

30, 20, 10

2. Create a class called LabStack

3. Create the following in LabStack:

   1. A static method called popN that takes a stack st and an integer n as parameters. This method pops n items from st and returns an ArrayList that contains all the values that were popped.

Example (result in red)

[30, 20]

2. A static method called popAll that takes a stack st as a parameter. This method pops all items from st and returns an ArrayList that contains all the values that were popped.

Example (output in red)

[30, 20, 10]

3. A static method called reverse that takes an int array arr as a parameter. This method creates a local stack variable, puts all values from arr into the stack, then pops them to store them in a new int array. It returns the new int array, which should contain all the values from arr reversed.

[50, 40, 30, 20, 10]

Answer 1

Stack.java

import java.util.ArrayList;

public class Stack {
private static final int MAX = 10;
private int index;
private int arr[] = new int[MAX];
  
public Stack()
{
this.index = -1;
}
  
public boolean isEmpty(){ return (this.index < 0); }
public boolean push(int num)
{
if(index >= (MAX - 1))
{
System.out.println("Stack Overflow!");
return false;
}
else
{
arr[++index] = num;
return true;
}
}
  
public int pop()
{
if(index < 0)
{
System.out.println("Stack Underflow!");
return 0;
}
else
{
int temp = peek();
arr[index] = -1; // assume, -1 signifies null
index--;
return temp;
}
}
  
public int peek()
{
if(index < 0)
{
System.out.println("Stack Underflow!");
return 0;
}
else
{
int temp = arr[index];
return temp;
}
}
  
public int getSize()
{
return (index + 1);
}
  
public int[] getStackArray(){ return this.arr; }
  
@Override
public String toString()
{
String out = "STACK: [";
if(index == -1)
{
out += "]\n";
return out;
}
  
ArrayList<Integer> list = new ArrayList<>();
for(int i = 0; i < arr.length; i++)
{
if(arr[i] > 0)
list.add(arr[i]);
}
  
for(int i = 0; i < list.size(); i++)
{
if(i == list.size() - 1)
out += list.get(i) + "]\n";
else
out += list.get(i) + ", ";
}
return out;
}
}

LabStack.java (Main class)

import java.util.ArrayList;
import java.util.Random;

public class LabStack {
  
public static void main(String[] args)
{
// create an instance of stack class
printMessage("Creating an instance of the Stack class..");
Stack stack = new Stack();
  
// generate 10 random numbers between 10 & 100 and push them to the stack
printMessage("\nGenerating 10 random numbers between 10 & 100 and pushing them to the Stack..");
Random rand = new Random();
for(int i = 0; i < 10; i++)
{
int pick = 10 + rand.nextInt(100);
while(pick < 10 || pick > 100)
pick = 10 + rand.nextInt(100);
stack.push(pick);
}
  
// display the initial contents of the stack
printMessage("\nInitial contents of the Stack..\n" + stack);
  
// now generate another random integer between 1 & (stack size / 2), for popping n values from the stack
int nVal = 1 + rand.nextInt(stack.getSize() / 2);
while(nVal < 1 || nVal > stack.getSize() / 2)
{
nVal = 1 + rand.nextInt(stack.getSize() / 2);
}
printMessage("\nPopping " + nVal + " integers from the stack..");
ArrayList<Integer> nValuesPopped = popN(stack, nVal);
printMessage(nValuesPopped + "");
printMessage("\nStack contents after popping " + nVal + " integers..\n" + stack);
  
// now reverse the stack containing the remaining integers
printMessage("Reversing the Stack contents..");
int[] arr = reverse(stack.getStackArray());
ArrayList<Integer> reversedList = new ArrayList<>();
for(int i = 0; i < arr.length; i++)
{
if(arr[i] > 0)
reversedList.add(arr[i]);
}
printMessage("STACK: " + reversedList);
  
// finally, we pop all the values from the stack
printMessage("\nPopping all the integers from the stack..");
ArrayList<Integer> nValuesPoppedAll = popAll(stack);
printMessage(nValuesPoppedAll + "");
printMessage("\nStack contents after popping all the integers..\n" + stack);
}
  
private static ArrayList<Integer> popN(Stack st, int n)
{
ArrayList<Integer> list = new ArrayList<>();
if(n > st.getSize())
{
System.out.println("n value exceeded stack size!");
return list;
}
  
for(int i = 0; i < n; i++)
{
list.add(st.pop());
}
return list;
}
  
private static ArrayList<Integer> popAll(Stack st)
{
ArrayList<Integer> list = new ArrayList<>();
while(!st.isEmpty())
{
int temp = st.pop();
if(temp > 0)
list.add(temp);
}
return list;
}
  
private static int[] reverse(int arr[])
{
Stack st = new Stack();
for(int i = 0; i < arr.length; i++)
st.push(arr[i]);
int reversedArray[] = new int[arr.length];
for(int i = 0; i < arr.length; i++)
{
int temp = st.pop();
if(temp >= 0)
reversedArray[i] = temp;
}
return reversedArray;
}
  
private static void printMessage(String msg)
{
System.out.println(msg);
}
}

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