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How can I change this linear Java Code for a program that adds and subtracts to Object-Oriented Code

I am trying to make a simple android app that can add and subtract numbers, but my challenge is to make sure that the program is Object-Oriented. Currently I have been told that it is linear, but I am confused as to how it has remained linear after trying many times to make it object-oriented. How can I make this object oriented programming. Here is my code.
import java.util.Scanner;
public class addNumbers {
public static void main(String[] args)
{ // Begin main
Scanner input = new Scanner( System.in ); // Instantiate object input
System.out.println("Enter number 1"); // Ask the user to enter number 1
double number1 = input.nextDouble(); // Read the first number
System.out.println("Enter number 2"); // Ask the user to enter number 2
double number2 = input.nextDouble(); // Read the second number
double sum=number1 + number2; // Add the numbers
double difference = number1 - number2; // Subtract number 2 from number1
System.out.printf("\nSum = %f\n", sum); // Print the sum
System.out.printf("Difference = %f", difference); // Print the difference.
}
} // end main

My applications use this boilerplate to execute inside an object. If you start like this, you can add methods as you need them.
public class Demo
{
public static void main (String[] args)
{
final Demo app = new Demo ();
app.execute ();
}
private void execute ()
{
// Do stuff here.
}
}

Whoever gave you this assignment is using wrong and confusing terms, because linear programming is something else. But that's a different topic.
Even though this program is not complex, we can introduce some classes by modelling the flow of the program and/or the math operations.
Here is one idea... we could have a class called Operands, that has a method to read the numbers from the input while it prints instructions to the output. Then it stores these two numbers.
So something like this (I am using static class here instead of just class in case you will put this inside your public class addNumbers)
static class Operands {
public final double first;
public final double second;
public Operands(double first, double second) {
this.first = first;
this.second = second;
}
public static Operands readFromIO(InputStream in, PrintStream out) {
Scanner input = new Scanner(in); // Instantiate object input
out.println("Enter number 1"); // Ask the user to enter number 1
double number1 = input.nextDouble(); // Read the first number
out.println("Enter number 2"); // Ask the user to enter number 2
double number2 = input.nextDouble(); // Read the second number
return new Operands(number1, number2);
}
}
Then we could have another class called Calculator, that has a method to set the operands setOperands(Operands operands) and two methods to get the results for the sum and the difference. The methods could be called getSum and getDifference.
static class Calculator {
private double sum = 0;
private double difference = 0;
public void setOperands(Operands operands) {
sum = operands.first + operands.second;
difference = operands.first - operands.second;
}
public double getSum() {
return sum;
}
public double getDifference() {
return difference;
}
}
Then in the main method of the program, we just need to make an instance of the Calculator class and set the Operands on the instance. We read these operators by calling Operands.readFromIO(...). Then we retrieve the sum and the difference from the calculator instance.
So the code in main looks like this
public static void main(String[] args) {
Calculator c = new Calculator();
Operands operands = Operands.readFromIO(System.in, System.out);
c.setOperands(operands);
System.out.printf("Sum = %f\n", c.getSum()); // Print the sum
System.out.printf("Difference = %f\n", c.getDifference()); // Print the difference.
}
This is just one way to do it with some objects.
Another way could be to use an interface called Operation that contains a calculate(Operands operands) method and have 2 more classes Addition and Subtraction implement the interface. Then you would use those two classes to calculate the results.

Tying to solve a problem regarding displaying shipping costs where one package is costlier than the other (Java)

I'm currently working on an assignment which takes input values from the user length, height, width calculates the volume, with a helper method that the base price for a package with volume <=1 is $3, and for every unit increase in volume, the cost increase is $1.
The code will display the cost of shipping for the two packages and output the difference between the two shipping costs.
Where I am stuck is I believe where I was confusing myself was one of the requirements is
i. if there is no difference, display the costs are the same.
ii. If the cost of one is less than twice the other, display that it is “slightly more than
iii.”If the cost of one is less than three times the other, display that it is “twice”
iv. If the cost of one is less than four times the other, display that it is “triple”
v. If the cost of one is less than five times the other, display that it is “quadruple”
vi. otherwise, display that it is the calculated multiple
public class Shipment {
private Package pack1, pack2;
private String message;
private NumberFormat currency = NumberFormat.getCurrencyInstance();
private DecimalFormat decimal = new DecimalFormat("#.##");
public Shipment() {
System.out.println("Welcome to Jaylen Carroll's shipping calculator!!");
this.pack1 = new Package();
this.pack2 = new Package();
message = "";
}// prints the title uses default constructor and
public void inputPackages() {
System.out.println("Enter first package dimensions");
inputPackage(this.pack1);
System.out.println();
System.out.println("Enter second package dimensions");
inputPackage(this.pack2);
}
public void inputPackage(Package pack) {
pack.inputLength();
pack.inputWidth();
pack.inputHeight();
}
public void calculateCost() {
double volP1 = pack1.calcVolume();
double volP2 = pack2.calcVolume();
double costPack1 = 3+(volP1-1);
double costPack2 = 3+(volP2-1);
System.out.println("Package 1 will cost "+costPack1);
System.out.println("Package 2 will cost "+costPack2);
if(volP1 == volP2) {
System.out.println("The shipping costs are the same.");
/* How can I get this if statement to print the cost difference and display which one is more expensive than the other.*/
}
public void display() {
System.out.print("First package dimensions: ");
this.pack1.displayDimensions();
//add memo about shipping
System.out.print("Second package dimensions: ");
this.pack2.displayDimensions();
//add memo about shipping
}
}

Is it something like this you're looking?
if(volP1 == volP2) {
System.out.println("The shipping costs are the same.");
}else if(volP1 < (2*volP2)){
double result = volP2 - volP1;
System.out.println("Package one is " +result +" cheaper than package two");
}

How to correlate an assigned String value to an Integer value?

I'm writing a code that allows the user to dictate what type of investment they want (Annual, Monthly or Quarterly) and each investment type correlates to a specific integer: i.e. Annual = 1, Monthly = 12, and Quarterly = 4. However when I assigned annual a value, I also need it to correlate to an int value in my investment equation below and am completely stumped on how to do so.
import java.util.Scanner;
import java.lang.Math;
public class CompoundInterest {
public static void main (String [] args)
{
Scanner cool = new Scanner (System.in);
double saving, rate;
int principal, years;
int choice;
System.out.println("Please enter you principal investment:");
/*Print statment prompts user to enter their principal investment*/
principal = cool.nextInt();
System.out.println("Would you like to have a regular investment plan?");
/* Print out statement asks user if they would like to participate in a regular investment plan*/
String question =cool.next();
System.out.println("What type of investment plan would you prefer (Annual, Quarterly, or Monthly)?");
String quest =cool.next();
while (quest.equalsIgnoreCase(("Annual")))
{ String Annual="1";
Annual.equals(choice);
}
System.out.println("Please enter the number of years that you wish to invest for:");
/* Print statement prompts user to enter the number of years that they wish to invest for*/
years = cool.nextInt();
System.out.println("Please enter the return rate per year:");
/* Print statement prompts user to enter the return rate per year*/
rate = cool.nextDouble();
saving = principal*(1+(rate/choice))* Math.pow(choice, years);
System.out.printf("%.2f", saving);
}

Once the type of investment plan is answered, you need to check if the quest variable matches any of the string you are expecting, i.e., Annual, Quarterly, or Monthly.
If the quest matches any of the choices, you assign a correct value to the choice variable, i.e., 1, 4, or 12.
You also may also need to think of situations if the answer doesn't match any of the correct choices.
if ("Annual".equalsIgnoreCase(quest)) {
choice = 1;
} else if ("Quarterly".equalsIgnoreCase(quest)) {
choice = 4;
} else if ("Monthly".equalsIgnoreCase(quest)) {
choice = 12;
} else {
//you need to do something here.
}

I would recommend using an enum that defines the int you want. I'll call the enum Plan and the int term:
public enum Plan {
ANNUAL(1),
QUARTERLY(4),
MONTHLY(12);
int term;
Plan(int term) {
this.term = term;
}
};
You would use this in your code like this (this replaces int choice):
Plan plan = Plan.valueOf(quest.toUpperCase());
saving = principal * (1 + (rate / plan.term)) * Math.pow(plan.term, years);
I think you are going to need different versions of your calculation. The enum approach would support this easily if you added a method to the enum that switches on the value of the enum. You can work out the different implementations of the calculation and define them in the case statements.
double calculateSavings(int principal, double rate, int years) {
switch (this) {
case ANNUAL:
case QUARTERLY:
case MONTHLY:
default:
return principal * (1 + (rate / term)) * Math.pow(term, years);
}
}
If you go this route you would use it in your code like this:
// saving = principal * (1 + (rate / plan.term)) * Math.pow(plan.term, years);
saving = plan.calculateSavings(principal, rate,years);

Input/Output - Arithmetic Equation

I am brand new to Java, started two weeks ago and am having issues wrapping my mind around this issue. I have a problem in a class I am taking that has been brought up before. Converting kilograms to pounds and rounding to the second decimal place.
I can create the input side of things and bring up a dialog box to prompt the user to enter in a weight. I can also create an output that uses an equation I made to output the answer in a dialog box.
My question is how do I take the information that is input and use it to convert from kilograms to pounds?
I have been reading my book and scouring the internet trying to find an answer and I think I may be over thinking it. Thanks for the help.
Input.java:
//This program asks a user to input a weight in kilograms.
package module2;
import javax.swing.*;
public class Input {
public static void main(String[] args) {
String weight;
weight = JOptionPane.showInputDialog("Enter weight in kilograms");
}
}
Output.java:
//This program outputs a converted weight from kilograms to pounds.
package module2;
import javax.swing.JOptionPane;
public class Output {
public static void main(String[] args) {
double kg = 75.5;
double lb = 2.2;
double sum;
sum = (kg * lb);
JOptionPane.showMessageDialog(null,sum, "Weight Conversion", JOptionPane.INFORMATION_MESSAGE);
}
}

Right now you have 2 main methods. Both of these are entry points for the program. Since they have to share information, it doesn't make sense you have both.
What I'd recommend is to change the Output's main method to a instance method, taking one parameter: the weight from the Input.
Like so:
public void printOutput(final double weight){
//...
}
You can then call that from the Input's main method like so:
public static void main(String[] args) {
String weight;
weight = JOptionPane.showInputDialog("Enter weight in kilograms");
double kg = Double.parseDouble(weight); // Be sure to parse the weight to a number
Output output = new Output(); // Create a new instance of the Output class
output.printOutput(kg); // Call our method to display the output of the conversion
}
One other thing, is that since Output is currently only used for that one method, you could consider just moving that method into Input.

// addition of two integers using JOptionPane
import javax.swing.JOptionPane;
public class Addition
{
public static void main(String[] args)
{
String firstNumber = JOptionPane.showInputDialog("Input <First Integer>");
String secondNumber = JOptionPane.showInputDialog("Input <Second Integer>");
int num1 = Integer.parseInt(firstNumber);
int num2 = Integer.parseInt(secondNumber);
int sum = num1 + num2;
JOptionPane.showMessageDialog(null, "Sum is" + sum, "Sumof two Integers", JOptionPane.PLAIN_MESSAGE);
}
}

How do I keep track of the balance on a bank account?

I am going to create a program that keeps track of the balance on a bank account. The program shall use a loop that continues until the user choses to exit by answering no to the question Do you want to continue?.
In the loop the user shall be asked to enter an amount (positive for deposit and negative for withdraw). The amount shall be added/subtracted from an account balance variable. All deposits/withdraws shall be saved as a history so that we can print it later. When the user choses to exit the loop the current account balance together with the account history (from the array/ArrayList) shall be printed.
Now, I want to use an array with ten slots for the history feature.
My question is how can I keep track of the all deposit, withdraw and current account balance (using an array with ten slots for the history feature) so that I can print it out while the user exits the program?
My code:
BankApp class:
package bankapp;
import java.util.Scanner;
public class BankApp {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
askingUser au = new askingUser();
System.out.println("WELCOME TO OUR BANK!\nYou have 100 SEK by default in your account.");
while (true) {
au.userInput();
System.out.println("Do you want to continue? Answer by Yes or No.");
String yesOrNo = input.next();
if (yesOrNo.equalsIgnoreCase("yes")) {
au.userInput();
} else if (yesOrNo.equalsIgnoreCase("no")) {
System.out.println("History: ");
//print out the transaction history
System.exit(0);
} else {
System.out.println("Invalid character input.");
}
}
}
}
askingUser class:
package bankapp;
import java.util.Scanner;
public class askingUser {
Scanner input = new Scanner(System.in);
double initialBal = 100;
public void userInput() {
System.out.println("Enter your amount: (+ve for deposit & -ve for withdraw)");
double inputAmount = input.nextDouble();
if (inputAmount >= 0) {
double newPosAm = initialBal + inputAmount;
System.out.println("Your current balance is: " + newPosAm + " SEK");
} else {
double newNegAm = initialBal + inputAmount;
System.out.println("Your current balace is: " + newNegAm + " SEK");
}
}
}

If you use an array, you have to keep track of the number of elements stored inside and resize the array when necessary. The easiest way would be to keep the history as strings in ArrayList. You would add one message to that list per transaction:
ArrayList<String> history = new ArrayList<String>();
void addToHistory(String transaction) {
history.add(transaction);
}
void printHistory() {
for(String s : history) {
System.out.println(s);
}
}
addToHistory("Withdrawal: 100 SEK" );
addToHistory("Deposit: 200 SEK" );
printHistory();

You need a queue to do that. However, for a simple, fast and primitive implementation you can:
Define an object called Transaction(deposit - double, withdraw - double, current account balance - double)
Add a List of Transactions into askingUser class as an attribute. I strongly recommend renaming the class name to AskingUser to make it seen as object.
At each operation add a new Transaction to end of the List you just added.
At exit, print out the last -say- 10 elements of the List; you can reach it through askingUser object. You can also define a function in askingUser class to print out the last 10 elements, if you make the function work according to selected number of elements, you can add number of Transactions to the function's inputs.