What is my mistake?

Question

Hi,
I made a Java code but something went wrong...

import java.util.Scanner ;
public class Program
{
public static void main(String[] args) {
Scanner java=new Scanner(System.in);
System.out.print("Data of ");
String readname=java.nextLine();
System.out.println(readname);
System.out .println();
if (readname==null ||readname.length()==0){
System.out.println("plz enter your name.") ;
}
if (readname=="John"){
System.out.println("hey!");
}
else{
}
}
}

I think that the mistake is somewhere here:
if (readname=="John"){
System.out.println("hey!");
}

But I didn't know what the mistake is. You should write in the input: John and then it should output "hey".

Answer 1

In most cases (except comparing primitive types), == operator performs referential equality: it returns 'true' if both references point to the same object, and 'false' otherwise. Take a look on a simple example which illustrates the differences:

final String str = new String("bbb");

System.out.println("Using == operator: "+ (str == "bbb") );

System.out.println("Using equals() method: "+ str.equals("bbb") );

From the human being prospective, there are no differences between str=="bbb" and str.equals("bbb"): in both cases the result should be the same as str is just a reference to "bbb" string. But in Java it is not the case:

Using == operator: false
Using equals() method: true

Even if both strings look exactly the same, in this example they exist as two different string instances.
**If you deal with object references, always use the equals() to compare for equality, unless you really have an intention to compare if object references are pointing to the same instance.

/*by Andriy Redko, "Advanced Java"*/

Answer 2

To compare two strings you have to use .equals()

If readname.equals("John")

https://www.sololearn.com/post/171078/?ref=app

Answer 3

Philipp Makarov
Your welcome :)

Answer 4

Thank you