This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 6 years ago.
I have two identical strings, one in an array and one in a String variable. When I compare these IDENTICAL strings I get false every time. I have debugged and debugged, but I get the same result every time. Here is the code in question
String temp = ""+(num1*num2);
Boolean equal = temp == answers[i];
if(equal) {
correct[i] = true;
num_correct ++;
}else{
correct[i] = false;
}
Again, I have debugged every minor detail of this program and I am 101% sure that the strings are IDENTICAL. Why is Java returning false on comparison?
When you use the == operator in Java with objects, you are attempting to compare object references. That is, is this object handle pointing to the EXACT same object as this other object handle. Unless the strings are interned, this will not work.
Use String.equals(Object) instead:
Boolean equal = temp.equals(answers[i]);
You are doing reference comparison, not value comparison. When you use the == operator its checking to see if the references are equal, and they aren't. If you want to check whether the values are equal use the equals method.
boolean equal = temp.equals(answers[i]);
== in java for strings is comparing to see if they are the same object, not the same string value. You should use .equals instead which will compare the value. == works sometimes because the strings can be interned and refer to the same object via reference even if created seperately through the same literal (so string b = "Hey" and string c = "Hey" end up being the same object in the background because "Hey" got interned to a hidden string object).
As others have shown you should use equals.
But I would also use the booleanValue of the Boolean object.
Here is your code correctly done
String temp = ""+(num1*num2);
Boolean equal = temp.equals(answers[i]);
if(equal.booleanValue()) {
correct[i] = true;
num_correct ++;
}else{
correct[i] = false;
}
Does this help?
Boolean equal = (temp == answers[i]);
I'm not sure that would be an issue, but I always enclose my conditions in parenthesis.
Related
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 4 years ago.
I am trying to check if a playlist is simple or master by an index value. My problem is when I put the (True) URL it still returns a false statement "This is a simple Playlist".
Any tips on how I can fix this ?
String output = getPlaylistUrl(input);
String mediaRecord = output.substring(399);
String lastRecord = "gear4/prog_index.m3u8";
if (mediaRecord == lastRecord) {
System.out.println("This is a master playlist");
} else {
System.out.println("This is a simple playlist");
}
In Java, strings can not be compared for equality using ==, because == compares two instances, not the content. So unless s1 and s2 are actually the same instance, s1 == s2 will never return true.
You need to use equals(...) to compare two strings for equality.
if (mediaRecord.equals(lastRecord) { ... }
In order to compare Strings you need to use .equals and not ==. Using == compares references and not values
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 9 years ago.
I am relatively new to coding in general and have run into an issue, I've looked everywhere for help but I cant find this issue. It would be greatly appreciated if someone could tell me why the string "s" doesn't ever equal the string "temp" even if I type the correct number in.
String s = null;
do{
s = (String) JOptionPane.showInputDialog(null, "Select a card to check for (Jacks = 11, Queens = 12, Kings = 13)", "Player's Turn", JOptionPane.PLAIN_MESSAGE, null, null, "Pick a card");
System.out.println(s);
for(int x = 0; x < PlayerCards.size(); x++){
String temp = PlayerCards.get(x).getFace();
if(s == temp){
playerhas = true;
}
}
if(s == null || playerhas != true){
JOptionPane.showMessageDialog(null, "Please pick a card you have.", "Error", JOptionPane.INFORMATION_MESSAGE);
}
}while(s == null || playerhas != true);
Strings work like objects in Java.
If you do stringA == stringB this will always return false since stringA and stringB are different objects.
Comparing strings needs to be done using stringA.equals(stringB) and this should return true (if the values match).
Chris 7 you're right that strings are objects but new compilers do some optimizations on those strings and it could happen that stringA == stringB are equal but it's not promised. So you should always use the string comparison functions (String.equals or String.equalsIgnoreCase).
By the way you can optimize your code. Use functions that implement only one feature and not more... e.g. externalize your function that checks if one has the card or not:
boolean playerHas(String s) { for (PlayerCard card : playerCards) { ... } return false; }
The
==
operator compares objects, while the
.equals
function compares object values.
String foo = "loremipsum";
String bar = "loremipsum";
System.out.println(foo == bar);
System.out.println(foo.equals(bar));
this ==compare bits, it works with primitive variable because when you declare a primitive variable it saves its value in bits, but when you declare a reference variable it only works if two reference are the same.
See this example:
String object1 = new String("hola");
String object2 = object1;
System.out.print(object1==object2);
This will return true because object2 have the same bits that point to the same object on heap, because they were copied when i said:object2 = object1
So if you want to compare objects by value instead by reference you have to use: equals() method.
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 9 years ago.
I am still new to Java. I am trying to create a program where users must answer a multiple choice quiz. The users will input their answer and these inputs will be formed into an array. Then I plan on using a for loop to compare the user's answers array to the array of correct answers to tell the user if they are right or wrong.
However it seems that i am not properly comparing the 2 arrays in my if statement. Every time I run the program, it goes straight to the else statements.
My hunch is that the scanner class does not actually store the value?
Can anyone help?
Part of code below:
//Above this section is just a collection of "System.out.println" statements that state questions and answers the user choose from.
int x;
String answers [] = {"a", "a", "b"};
//answers array has the correct answer
Scanner in = new Scanner(System.in);
String answerEntered [] = new String [5];
//user input will be in this arra
for(x=0 ; x<3 ; x++)
{
System.out.print((1+x)+". ");
answerEntered[x] = in.nextLine();
}
for( x=0; x<3; x++)
{
**if(answerEntered[x] == answers[x])
{
System.out.println("For Question "+(x+1)+", you are Correct!");
}**
//This if section does not seem to work. Every time i run the code it automatically goes to the else statement.
else
{
System.out.println("The correct answer for Question "+(x+1)+" is: "+answers[x]);
}
}
In Java, String aren't primitive values, you have to use String.equals() to compare strings
so, change this:
if(answerEntered[x] == answers[x])
to
if(answerEntered[x].equals(answers[x]))
I would also suggest that you check for nullability and ignore case, so:
String answer = answerEntered[x];
boolean isAnswerCorrect =
answer != null &&
//remove trailling spaces and ignore case (a==A)
answer.trim().equalsIgnoreCase(answers[x]);
if(isAnswerCorrect){
For String or any object-equality test in Java, you should almost always be using equals. The == operator only compares references when used with objects (but will work the way you expect it to with primitives like int, boolean, etc); that is, it checks to see if the operands both point/refer to the same object instance. What you're interested in doing is comparing the contents of the String instance, and equals will do that for you:
if(answerEntered[x].equals(answers[x])) {
...
}
For String comparison, you need to use equals instead of ==, which for non-primitive data types, such as String, compares their references, not values.
String a = "foo";
String b = "bar";
if (a.equals(b))
{
//doSomething
}
The problem is in the comparison :
String a = "foo";
String b = "bar";
if (a.equals(b))
//doSomething
AS it Has been answered before.
Extra information, in the for loop of the if / else you are looping only the first 3 positions, not the 5 that exists in the answerEntered array.
Cheers
Use .equals to compare strings. equals compares the values, where == compares the reference
.
In Java, == comparison compares reference identity, means the two things you compare must be the same object. Two objects with the same values are treated as different.
You statement:
if(answerEntered[x] == answers[x])
The answerEntered contains string that is different with any string in answer even if they have the same value.
Java uses Object's .equals method to compare by value, i.e. Two objects are equal as long as they have the same value.
Changing:
if(answerEntered[x] == answers[x])
to
if(answerEntered[x].equals(answers[x]))
should solve the problem.
Also, as answerEntered contains user inputed value, you'd better pre-process it before using it. For example, user might put answer "a " with spaces at the end. You might want to get rid of those spaces as well.
Otherwise "a " will be treated as an incorrect answer.
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 9 years ago.
How do I know if String letter is equal to char array
String[] choose = {"a","d","t","b","s","f","x"};
String check;
boolean error = false;
System.out.print("Enter");
Scanner sn = new Scanner(System.in);
check = sn.nextLine();
for (int i = 0 ; i < choose.length;i++){
if(choose[i] == check){
System.out.print("you entered" + choose[i]);
break;
}
}
What I did is this it didnt confirm I input letter a but "you entered" didnt show up.
You cannot test strings for equality using ==. That only compares references (memory addresses). You need to use String#equals(Object). In general == is most certainly what you don't want if you are testing for equality, unless you are checking to see if two variables are pointing to the same instance. This is rarely the case, since you are usually interested in testing values for equality.
So what you need to do is:
if(choose[i].equals(check)) {
...
}
You are trying to compare strings with ==, which only compares the references, but not the values. What you want to use is
if(check.equals(choose[i]))
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
String is not equal to string?
What makes reference comparison (==) work for some strings in Java?
can some one explain me following java code
String a = "1";
if(a == "1") {
//print compare 1 is true;
} else {
//print compare 1 is false;
}
if(a.equals("1")) {
//print compare 2 is true;
} else {
//print compare 2 is false;
}
it results like
compare 1 is false
compare 2 is true
Only explanation i have is that its comparing the memory address not the values itself. But i am not sure. can some please put a light on it. in .Net == operator is overloaded to compare contents of string.
use "1".equals(a) , String is an object so use equals() to compare
I understood that == operator is compare "Is it same object?"
object a is not same object with constant string "1".
so returns false