display triangle by comparing values of sides stored as a list of strings

Question

I have split the list of strings by "," and then checked the charAt 0==1 and charAt 0==2 then equilateral triangle....so on, but i am getting none of these for all, while debugging i can see the charAt 0 and charAt 1 are equal bt the entire evaluation is false.


    public static void main(String[] args) {
        List<String> triangleToy=Arrays.asList("36 36 36","3 3 3","2 4 2");
         List<String> toRet= new ArrayList<String>();
        // TODO Auto-generated method stub
        for (String s : triangleToy) {

        String[] index=s.split(" ");

        if((index[0]==(index[1]))&&(index[0]==(index[2]))){

            toRet.add("Equilateral");

        }
        else if(index[0]==(index[1])){
            toRet.add("Isosceles");

        }
        else{
            toRet.add("None of these");
        }


    }
        System.out.println(toRet);

}
}

Please explain me whats going on here...

Strings in Java are compared with the equals function ;) – maio290 Mar 23 '20 at 07:37 — maio290, Mar 23 '20 at 07:37

score 1 · Answer 1 · answered Mar 23 '20 at 07:42

When comparing Strings in Java (and, more generally, objects) with the "==" operator, what is compared is not the characters of the Strings but their reference. If the two objects are not the very same object, "==" returns false

Here, you should modify your for loop this way:

for (String s : triangleToy) {

    String[] index=s.split(" ");

    if((index[0].equals(index[1]))&&(index[0].equals(index[2]))){

        toRet.add("Equilateral");

    }
    else if(index[0].equals(index[1])){
        toRet.add("Isosceles");

    }
    else{
        toRet.add("None of these");
    }


}

For Strings, the .equals function compares the characters in the strings rather than their references.

sgX · Accepted Answer · 2020-03-23T08:31:50.283

I see two issues in your program:

As already pointed out, == compares the reference which is not reliable in your case of string comparision, it is also not the recommended way you compare strings in Java, index[0].equals(index[1]) and likewise would do it for you. Look at this answer for more details.
In the 'Isoceles' control statement, you need to have additional conditions like this: index[0].equals(index[1]) || index[1].equals(index[2]) || index[0].equals(index[2])

display triangle by comparing values of sides stored as a list of strings

2 Answers2