小编use*_*720的帖子

我正在尝试创建一个基本calculator的Java.我对编程很陌生,所以我试着习惯它.

import java.util.Scanner;
import javax.swing.JOptionPane;

public class javaCalculator 
{

    public static void main(String[] args) 
    {
        int num1;
        int num2;
        String operation;


        Scanner input = new Scanner(System.in);

        System.out.println("please enter the first number");
        num1 = input.nextInt();

        System.out.println("please enter the second number");
        num2 = input.nextInt();

        Scanner op = new Scanner(System.in);

        System.out.println("Please enter operation");
        operation = op.next();

        if (operation == "+");
        {
            System.out.println("your answer is" + (num1 + num2));
        }
        if  (operation == "-");
        {
            System.out.println("your answer is" + (num1 …

public void listAllFiles() {
    for (String filename: files) {
        int position = 0;
        System.out.println(position + ": " + filename);
        position = position + 1;
    }
}

上面的循环显示来自的元素ArrayList files.我想显示索引以及列表中的字符串元素.但是,调用该方法时,索引始终显示为"0".