How to search for the variable name of a String in an ArrayList

Question

Hello I am new to Java and had a quick question about looking for the name of a String in an ArrayList. Here is the code I wrote:

import java.util.*;
public class Rubix{

    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        String input;
        String FRS="U (R U' R')";
        String RBS="y' U' (R' U R)";
        String FLD="y' (R' U' R)";
        ArrayList RA = new ArrayList();
        RA.add(FRS);
        RA.add(RBS);
        RA.add(FLD);

        System.out.println("Name the situation.");
        input=sc.nextLine();
        for(int i=0; i<RA.size(); i+=1){
            if (input==RA.get(i)){
                System.out.println(RA.get(i));
            }
        } 
    }
}

What I am asking for help with is writing the if statement. I want to test to see if that name for the String is within the ArrayList. I know what I have currently is wrong so please help.

if (RA.contains(input)), also, = is assignment, not comparison — MadProgrammer
– MadProgrammer, Commented Jan 5, 2016 at 2:43

Steven K · Accepted Answer · 2016-01-05 02:47:48Z

1

You can try :

If (input.equals(RA.get(i)))

Also at end of for statement it should be I++ not I+=1

answered Jan 5, 2016 at 2:47

Steven K

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Comments

Josh Kitchens · Accepted Answer · 2016-01-05 02:51:04Z

When you add an item to a list, you're not adding the variable itself to the list to be referenced by name later. Rather, you're copying the value of that variable into the list.

In your case, after

RA.add(FRS);

RA does not contain the text "FRS". It has no idea what "FRS" is. What it DOES contain, is the value of FRS, in this case, a String with the value "U (R U' R')", stored in the first position (index 0) of the list.

It also looks like you're trying to take an input and match it against the list of values in the array. But this line:

if (input=RA.get(i)){

has a bug. A single "=" is the assignment operator, used to assign values on the right to variables on the left. So in your case, when the code executes this if check, it's actually ASSIGNING the value of RA.get(i) into input, overriding the input value. Assignments return "true" if they succeed, and since this one can't fail, it will always be true.

When comparing strings in java, you need to use the ".equals()" method that every String object has. So in your case, your line should read:

if (input.equals(RA.get(i)){

Ruchir Baronia · Accepted Answer · 2016-01-05 02:45:14Z

0

1. Loop through 2. Compare arraylist using `contains` method

for (int i = 0; i < list.size(); i++) {
 System.out.println(list.get(i));
 if (list.contains(inputstring)) { 
// You have found a mach! 
}
 }

The contains method just checks whether your list contains the string which is put into the paramater. You call the method on your array[list] object.

answered Jan 5, 2016 at 2:45

Ruchir Baronia

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Comments

Pritam Banerjee · Accepted Answer · 2016-01-05 02:47:18Z

0

This is how your code should be like :

private static Scanner sc;

public static void main(String[] args) {
    sc = new Scanner(System.in);
    String input;
    String FRS="U (R U' R')";
    String RBS="y' U' (R' U R)";
    String FLD="y' (R' U' R)";
    ArrayList<String> RA = new ArrayList<String>();
    RA.add(FRS);
    RA.add(RBS);
    RA.add(FLD);


    System.out.println("Name the situation.");
    input=sc.nextLine();
    for(int i=0; i<RA.size(); i= i+1){
        if (input.equals(RA.get(i))){
            System.out.println(RA.get(i));
        }
    }


}

answered Jan 5, 2016 at 2:47

Pritam Banerjee

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Comments

TangledUpInBlue · Accepted Answer · 2016-01-05 03:10:42Z

-1

ArrayList has a contains method, so just do this:

if (RA.contains(input)) {
  // do stuff
}

edited Jan 5, 2016 at 3:10

answered Jan 5, 2016 at 2:43

TangledUpInBlue

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2 Comments

numbersFTW Over a year ago

doesn't the contain method just search through the list the String in the arrayList and not the objects holding the strings. And sorry for some of the errors, I kinda made this in like a minute just so I could ask this question

TangledUpInBlue Over a year ago

The ArrayList is holding Strings, not another kind of object. You should probably make this explicit in your constructor: ArrayList<String> RA = new ArrayList();

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