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In Java, what is the functional difference between using the "==" operand and the "variable.equals(param)? [duplicate]

This question already has answers here:
What is the difference between == and equals() in Java?
(26 answers)
Closed 10 months ago.
I am within my first year of CS and near the end of my first Java themed course so I'm not quite sure how to find the answer to my question myself.
While writing some code for a project I created my input scanner as:
Scanner scanner = new Scanner(System.in);
I am taking user inputs as strings via a variable assignment:
String userInput = scanner.nextLine();
the user should only be entering strings of char "1" - "6" and "q" (to quit app)
What I'm using that works currently is as follows:
userInput = scanner.nextLine();
while (!appQuit) { //So long as user doesn't quit application
if (userInput.equals("q")) {
appQuit = true;
}
else if (userInput.equals("1")) { //Menu selection for intake a new dog
intakeNewDog(scanner);
displayMenu();
userInput = scanner.nextLine();
}
//removed "2" - "6" for brevity
else {
System.out.println("Not a valid input");
displayMenu();
userInput = scanner.nextLine();
}
}
The only way I found to check equality was the userInput.equals() function.
When I originally wrote it I tried using:
if (userInput == "1") { code }
but it would never successfully compare values as I thought it would.
Any insight into why one method works over the other? Or where I should be looking for these answers?
-Jonesy

The == equal operator compares the object references where the equals function compares the value.
For primitive types and enums the == equal operator compares the value.
An exception happens for comparing strings in a switch case statement since it internal uses the equals method.
As a rule of thumb, always use equals comparison for String. There maybe is, but i have not seen a case where reference comparison was important.
https://docs.oracle.com/javase/8/docs/technotes/guides/language/strings-switch.html
Also interesting:
What makes reference comparison (==) work for some strings in Java?

In simple words, == checks if both objects point to the same memory location whereas . equals() evaluates to the comparison of values in the objects. You can override the equals method to do more specific things, but that's the just of it.
This is literally the first thing that appears if you search java == vs equals in google.
While you might be trying to compare two strings, the operator == does not behave in java as it does in other languages.

Java String Conditional Break Not Working [duplicate]

This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 8 years ago.
I wrote a simple program which prompts the user to enter a sentence, word, or number, and then prints input is art. I put the program on an infinite loop so that the prompt would repeat. However, now I'm trying to add a way to quit by saying if (input == "quit") break; however it does not seem to be working. It just continues the infinite loop. Here is the full code:
import java.util.Scanner;
public class Art
{
public static void main(String [] args)
{
Scanner input = new Scanner(System.in);
String a;
for ( ; ; )
{
System.out.println("Please enter something: ");
a = input.nextLine();
if (a == "quit") break;
System.out.print("\n");
System.out.println(a + " is art.");
System.out.print("\n");
}
}
}
Any help would be lovely, thanks!

Use input.equals("quit").
The == is used to check whether two objects are the exact same instance - the same thing in memory -which the typed word and the constant string "quit" are not. Two instances of "quit" were created: one typed by the user, and one constant in the program.
The equals() method is used to compare whether two objects are equal in whatever way equality is defined for them. For strings, that would mean having the same text.
The difference between == and equals() is really fundamental in Java, so you should go over it. Here's a good SO post on the topic. Once you start creating your own classes, you will probably be implementing equals() methods for them. For that reason, make sure to go over the equals() / hashCode() contract as well.

looks like the a == "quit" is the problem. Compare strings using equals()
if("quit".equals(a)) {
}

Cannot create test condition after using nextLine() [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Java String.equals versus ==
I have been having difficulties using nextLine() to get a string, and then use it as a test condition (either in an if statement or a while loop). Looking at the println(), it seems as if the String is correctly assigned to the variable 'repeat' but then the test condition fails for some reason. Banging my head on the wall, bleeding from my forehead. Please help.
import java.util.Scanner;
public class potpie {
public static void main(String args[]){
Scanner input = new Scanner(System.in);
String repeat = "yes";
System.out.println("Type in yes");
repeat = input.nextLine();
System.out.println("If repeat is now yes, print yes: " +repeat);
if(repeat == "yes"){
System.out.println("It worked");
} else
System.out.println("it failed");
}
}

You should use equals. == provide you reference equality and equals provide you value equality.
if("yes".equals(repeat)){
instead of
if(repeat == "yes"){
I would advice you to get eclipse/net beans and start debugging or a simple search would have resulted in the answer
Java Debugging with Eclipse - Tutorial

if(repeat == "yes"){
should be
if(repeat.equals("yes"){
(or)
if("yes".equals(repeat){
Every day we see this question lot of times, simple search could have provided you sufficient information.
== equals for primitive comparison (reference equality). equals() is for String (or) Object comparison (object content equality).

Sometimes == should be used for objects, but what it is actually comparing is whether a and b are literally the same object (have the same address in memory). As the others have said, you are comparing content in this situation, so you use .equals()

Can't break the while loop [duplicate]

This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 5 years ago.
public void play () {
int anInteger;
//guess return code
int code;
while (true) {
String input=null;
input = JOptionPane.showInputDialog("Please enter an integer");
if (input == "-1") {
//JOptionPane.showMessageDialog(null, input);
System.exit(0);
break;
} else {
if (input==null) {
System.exit(0);
} else if (input.isEmpty()) {
continue;
} else {
anInteger = Integer.parseInt(input);
code = this.oneGuess (anInteger);
//JOptionPane.showMessageDialog(null, anInteger);
}
}
}
}
I want, if the user enter -1, show the program will not prompt the message box any more. Above is the code I have come up with, so far. Why it doesn't work?

String comparisons does NOT work with "==" operator, use "String.equals(Object)" function
input.equals("-1");
Better way would be
"-1".equals(input);
as it also takes care of null input

You are comparing strings, which are objects, with the == operator, which checks whether two object references refer to the same object instance. Instead you should use the equals method for comparing them.

There is a difference between comparing with == and equals. The first compares pointers, the latter contents. That is probably your issue.

You compare Strings with ==, which creates a problem. You can have many different String-Objects which all show "-1". The == tests, if you have exactly the same object on the left and right side. You want to know, if the objects on the left and right sie have an equal content.
Better try
input.equalsIgnoreCase("-1");
EDIT: To answer the comment: input.equalsIgnoreCase("-1") is the same as input.equals("-1") in the case of "-1" as there are no uppercase/lowercase letters in "-1". However, I prefer equalsIgnoreCase in the case of Strings, because it is defined on String, rather than on Object. Still, as the equals-definition is overridden for the String class, it works too in this example and "ignoreCase" is not needed.

Java Scanner Class [duplicate]

This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 4 years ago.
I am writing a program that should close the console if the user input the String "end'.
The program always performs the else loop even if the user inputs "end". I'm wondering why the program is not getting into the if part of the loop and shutting down.
Scanner scan = new Scanner(System.in);
while(true)
{
String num = scan.nextLine();
if(num == "end")
{
System.exit(0);
}
else
{
System.out.println("hi");
}
}

You're using == instead of "end".equals(num)

Don't use == for equality of string as it compares the objects not the string itself.
Use num.equals("end") or num.equalsIgnoreCase("end") if you want to be able to type end or END
I would not use "end".equals(num), although considered better from a performance perspective in most cases, it does not clearly state the business requirement and it is more important to make it more readable.
But be aware of num being null, if that is possible, num.quals("end") could throw an exception and you should write if (num!=null && num.equals("end")) { ... }
Note that "end".equals(num) does not need the null check, but I still believe this is not very readable, so I would go with if (num!=null && num.equals("end")) { ... }

For testing equality between strings, you should use equals() instead.
if(a.equals(b)) and so on.
This should help you out: http://leepoint.net/notes-java/data/expressions/22compareobjects.html

In Java, you test equality of strings with:
string1.equals(string2);
So in this case, it would be:
num.equals("end");
Or to avoid an exception of type NullPointerException:
"end".equals(num);

num refers to the object, so num == "end" should never be. You want num.equals("end")

Please do not use comparison (==) operator when comparing objects in Java. Use equals(Object) instead.