Getting the sum of elements of a HashSet (Java)

Question

** I am not sure how to get the sum of certain elements from a hashset please help** i need to add the amount from the expense

i am not sure about the line - System.out.println("Total Amount Spent:"+ set1.addAll([1]);

This is my code and the required output is also give below:

import java.util.*;

class Expense implements Comparable<Expense>{
    
    String expenseCategory;
    Integer amount;
    
    
    public String getExpenseCategory() {
        return expenseCategory;
    }
    public void setExpenseCategory(String expenseCategory) {
        this.expenseCategory = expenseCategory;
    }
    public Integer getAmount() {
        return amount;
    }
    public void setAmount(Integer amount) {
        this.amount = amount;
    }
    
    
    
    public Expense(String expC , Integer amount) {
        this.expenseCategory=expC;
        this.amount = amount;
    }
    
    
    public String toString() {
        return expenseCategory+ " " +amount;
    }
        
    
    public int compareTo(Expense e) {
        if(amount>e.amount){    
            return 1;    
        }else if(amount<e.amount){    
            return -1;    
        }else{    
        return 0;    
        } 
    }
}

public class Main {
    
    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        TreeSet<Expense> set1 = new TreeSet<Expense>();
        
        while(true) {
            System.out.println("Enter expense category");
            String expC = sc.next();
            System.out.println("Enter expense amount");
            String amt = sc.next();
            set1.add(new Expense(expC,Integer.valueOf(amt)));
            System.out.println("Do you want to continue(yes/no):");
            String cond = sc.next();
            if(cond.equals("no")) {
                break;
            }
        }
            System.out.println("Top spending categories");
            System.out.println("Category    Amount");
            Iterator x = set1.descendingIterator();
            
            while(x.hasNext()) {
                System.out.println(x.next());
            }
            
            
            System.out.println("Total Amount Spent:"+ set1.addAll([1]);//please help me figure out this part 
        
        
    }
    
}

OUTPUT Should be like:

Enter expense category
Rent
Enter expense amount
6000
Do you want to continue(yes/no):
yes
Enter expense category
Food
Enter expense amount
4500
Do you want to continue(yes/no):
yes
Enter expense category
Travel
Enter expense amount
2300
Do you want to continue(yes/no):
yes
Enter expense category
Mobile
Enter expense amount
700
Do you want to continue(yes/no):
no
Top spending categories
Category    Amount
Rent    6000
Food    4500
Travel    2300
Mobile    700
Total amount spent: 13500

Answer 1

Temporarly i added : a int variable in main class which will sum up the values every time i enter the amount and display it at the end.

class main{
    ...
    int tamount=0;
    ...
    tamount = tamount + Integer.valueOf(amt);

    ...
    System.out.println("Total Amount Spent:"+ tamount);
}

Answer 2

addAll is used to add elements from a Collection to the Set. You can use IntStream#sum in this case.

set1.stream().mapToInt(Expense::getAmount).sum()