从阵列中删除第一个元素

Question

right now I have an ArrayList of Strings. The array is filled with data the user enters in the console. I am trying to remove the first element of the array, and then use the rest of the input. By the rest of the input I mean the input without the first element. I am trying to do this by using nameofarray.remove(0); but that does not seem to be working. Any help on removing the first element of the array and then getting the rest of the array is appreciated, thanks!

import java.util.ArrayList;
import java.util.Scanner;

class Driver {

    public static void main(String[] args) {
        Scanner k = new Scanner(System.in);
        String userInput;
        char msb;
        int convertedBinary;
        String removedMSB;
        ArrayList<String> binaryInput = new ArrayList<String>();
        System.out.println("Press 1 to use the Binary Converter: Press 2 to use the Decimal Converter:");
        int userChoice = k.nextInt();

        if (userChoice == 1) {
            System.out.println("Welcome to the Binary Converter!");
            System.out.println("Please enter a 10 bit binary number");
            // Adding the input to the ArrayList
            userInput = k.next();
            msb = userInput.charAt(0);
            binaryInput.add(userInput);

            if (msb == '0') {
                convertedBinary = Integer.parseInt(userInput, 2);
                System.out.println("Your number in decimal is " + convertedBinary);
            } else if (msb == '1') {
                // Attempting to remove first element from ArrayList
                binaryInput.remove(0);
            convertedBinary = Integer.parseInt(userInput, 2);
            System.out.println("Your number in decimal is " +      convertedBinary);
            }
        }
    }
}

Answer 1

Your objective is very simple and you need not make use of ArrayList in this case.

When msb == '1' , remove the first character and then do the conversion. That's it. :-)

import java.util.Scanner;

class Driver {

    public static void main(String[] args) {
        Scanner k = new Scanner(System.in);
        String userInput;
        char msb;
        int convertedBinary = 0;

        System.out.println("Press 1 to use the Binary Converter: Press 2 to use the Decimal Converter:");
        int userChoice = k.nextInt();

        if (userChoice == 1) {
            System.out.println("Welcome to the Binary Converter!");
            System.out.println("Please enter a 10 bit binary number");
            userInput = k.next();
            msb = userInput.charAt(0);

            if (msb == '0') {
                convertedBinary = Integer.parseInt(userInput, 2);
            } else if (msb == '1') {
                convertedBinary = Integer.parseInt(userInput.substring(1), 2);
            }
            System.out.println("Your number in decimal is " + convertedBinary);
        }
    }
}

Answer 2

binaryInput.add(userInput);

BinaryInput is an ArrayList of strings. You're adding the string userInput into binaryInput, so now binaryInput[0] is the string userInput.

binaryInput.remove(0);

This line will remove the first element of binaryInput- which is userInput. I assume you only want to remove the first character of userInput, not the entire string as you're doing in your code right now.

I would suggest doing something like this instead:

public static void main(String[] args) {
    Scanner k = new Scanner(System.in);
    String userInput;
    char msb;
    int convertedBinary;
    String removedMSB;
    ArrayList<String> binaryInput = new ArrayList<String>();
    System.out.println("Press 1 to use the Binary Converter: Press 2 to use the Decimal Converter:");
    int userChoice = k.nextInt();

    if (userChoice == 1) {
        System.out.println("Welcome to the Binary Converter!");
        System.out.println("Please enter a 10 bit binary number");
        // Adding the input to the ArrayList
        userInput = k.next();
        String withoutFirstChar = userInput .substring(1);
        msb = userInput.charAt(0);

        if (msb == '0') {
            convertedBinary = Integer.parseInt(userInput, 2);
            System.out.println("Your number in decimal is " + convertedBinary);
        } else if (msb == '1') {
            convertedBinary = Integer.parseInt(withoutFirstChar , 2);
            System.out.println("Your number in decimal is " +      convertedBinary);
        }
    }
}

}

Answer 3

What do you mean by "is not working"? Is it producing an error? Using .remove(0) should work, I just made a little test and it removed the first element as expected. The output from the below code is [b, c] .

ArrayList<String> list = new ArrayList<String>();
list.add("a");
list.add("b");
list.add("c");
list.remove(0);
System.out.println(list);

Answer 4

This line in your else block

convertedBinary = Integer.parseInt(userInput, 2);

should be something like

convertedBinary = Integer.parseInt(binaryInputJoined, 2);

Where you will need to join the values you have in the binaryInput list.

It looks like you were either removing from the wrong list, or converting the wrong list. Alternatively you could avoid lists and use substring.