Java ArrayIndexOutOfBoundsException when reading user input

Question

Whenever I try to use anything higher than eq[0], I end up with an ArrayIndexOutOfBoundsException.

My code:

import java.util.Scanner;

public class Calc{
    public static void main(String[] args){
        Scanner in=new Scanner(System.in);
        String[] eq=in.next().split(" ");

        double a=Double.parseDouble(eq[0]);
        double b=Double.parseDouble(eq[-1]);

        if(eq[1]=="+"){
            System.out.println(">>"+String.valueOf(a+b));
        }else if(eq[1]=="-"){
            System.out.println(">>"+String.valueOf(a-b));
        }else if(eq[1]=="/"){
            System.out.println(">>"+String.valueOf(a/b));
        }else if(eq[1]=="*"){
            System.out.println(">>"+String.valueOf(a*b));
        }
    }
}

@Tunaki @sᴜʀᴇsʜ ᴀᴛᴛᴀ I tried `eq[2]` and got the same error — Valkyrie, Sep 29 '15 at 11:55
don't compare string with `==` instead you must use `equals()` — Rustam, Sep 29 '15 at 12:00

score 1 · Accepted Answer · edited Jun 20 '20 at 09:12

eq[-1] -1 index is problem

eq[1]=="+" // logical error use equals() method to compare String.

           Scanner in=new Scanner(System.in);
            String[] eq=in.nextLine().split(" "); // use nextLine() instead of next().
        
            double a=Double.parseDouble(eq[0]);// 1st operand
            double b=Double.parseDouble(eq[2]);// 3rd operand

            if(eq[1].equals("+")){ //operator // compare string with equals method not with (==).
                System.out.println(">>"+String.valueOf(a+b));
            }else if(eq[1].equals("-")){
                System.out.println(">>"+String.valueOf(a-b));
            }else if(eq[1].equals("/")){
                System.out.println(">>"+String.valueOf(a/b));
            }else if(eq[1].equals("*")){
                System.out.println(">>"+String.valueOf(a*b));
            }

score 0 · Answer 2 · answered Sep 29 '15 at 13:48

0

Firstly, eq[-1] the index should not be valid. I think it is only valid for Python. Secondly, when you want to compare 2 strings, you should not use ==. .equals function will help.

answered Sep 29 '15 at 13:48

Li Junbo

1
1

Java ArrayIndexOutOfBoundsException when reading user input

2 Answers2