Object comparison: Address vs Content

Hey guys im just messing around and I cant get this to work:

public static void main(String[] args){
    Scanner input = new Scanner (System.in);
    String x = "hey";
    System.out.println("What is x?:  ");
    x = input.nextLine();
    System.out.pr开发者_运维技巧intln(x);
    if (x == "hello")
        System.out.println("hello");
    else
        System.out.println("goodbye");
}

it is of course supposed to print hello hello if you enter hello but it will not. I am using Eclipse just to mess around. A little quick help please

Should be if (x.equals("hello")).

With java objects, == is used for reference comparison. .equals() for value comparison.

Don't use == when testing for equality of non basic types, it will test for reference equality. Use .equals(..) instead.

Look at the following diagram:

When using == you're comparing the addresses of the boxes, when using equals you're comparing their content.

You can't compare a string like that.Because String is a class.So if you want to compare its content use equals

 if (x.equals("hello"))
        System.out.println("hello");
    else
        System.out.println("goodbye");

x=="hello" compares the references not values , you will have to do x.equals("hello").

String s = "something", t = "maybe something else";
    if (s == t)      // Legal, but usually WRONG.
    if (s.equals(t)) // RIGHT
    if (s > t)    // ILLEGAL
    if (s.compareTo(t) > 0) // CORRECT>

Use "hello".equals(x) and never reverse since it does not handle null.

== operator checks equality of references (not values). In your case you have 2 String type object which have different reference but same value "hello". String class has "equals" method for checking values equality. The syntax is if(str1.equals(str2)).

Try this as the comparison:

if (x.equals("hello"))

Use x.equals("hello");

http://leepoint.net/notes-java/data/expressions/22compareobjects.html

Take this sample program:

public class StringComparison {
    public static void main(String[] args) {
        String hello = "hello";
        System.out.println(hello == "hello");

        String hello2 = "hel" + "lo";
        System.out.println(hello == hello2);

        String hello3 = new String(hello);
        System.out.println(hello == hello3);
        System.out.println(hello3.equals(hello));
    }
}

Its output would be:

true
true
false
true

Objects hello and hello3 have different references that's why hello == hello3 is false, but they contain the same string, therefore equals returns true.

The expression hello == hello2 is true because Java compiler is smart enough to perform concatenation of two string constants.

So to compare String objects, you have to use equals method.