Java comparison with == of two strings is false? [duplicate]

Answer 1

The == operator compares the object references, not the value of the Strings.

To compare the values of Strings, use the String.equals method:

"231".equals(parts[0]);

This is true with any other object in Java -- when comparing values, always use the equals method rather than using the == operator.

The equals method is part of Object, and should be overridden by classes which will be compared in one way or another.

Answer 2

== in Java compares the address of the objects (strings in this case).

What you want is parts[0].equals("231")

Answer 3

You may also use compareTo(String) method:

String str = "test";

if( str.compareTo("test") == 0)
   //the argument string is equal to str;
else
   //the argument string is not equal to str;

Answer 4

Use the equals method to compare objects:

String[] test = {"231", "CA-California", "Sacramento-155328", "aleee",
                 "Customer Service Clerk", "Alegra Keith.doc.txt"};

System.out.println("231".equals(test[0]));

The comparison '==' compares references, not values.

Answer 5

The following prints out "true";

String s = "231";
if(s == "231")
{
    System.out.println("true");
}
else
{
    System.out.println("false");
}

This is because Strings are not mutable and java will try and save as much space as possible, so it points both to the same memory reference.

However, the following prints out "false":

String s = new String("231");
if(s == "231")
{
    System.out.println("true");
}
else
{
    System.out.println("false");
}

new will force it to store the string in a new memory location.

By the way, you should ALWAYS use .equals() to compare strings (for cases just like this one)

Answer 6

Here's really nice example. The '==' operator with string can be really tricky in Java.

class Foo {
    public static void main(String[] args) {
        String a = "hello";
        String b = "hello";
        String c = "h";
        c = c + "ello";

        String operator = null;

        if(a == b) {
            operator = " == ";
        } else {
            operator = " != ";
        }

        System.out.println(a + operator + b);

        if(a == c) {
            operator = " == ";
        } else {
            operator = " != ";
        }

        System.out.println(a + operator + c);

        if(a == "hello") {
            operator = " == ";
        } else {
            operator = " != ";
        }

        System.out.println(a + operator + "hello");

        if(c == "hello") {
            operator = " == ";
        } else {
            operator = " != ";
        }

        System.out.println(c + operator + "hello");
    }
}

Which will produce following output:

hello == hello
hello != hello
hello == hello
hello != hello