Never thought I will be asking such a trifle query!
Please help with this stack:
if(request.getParameter("cl")=="star"){
txtFilePath = session.getServletContext().getRealPath("/cl.json");
}
else
{ txtFilePath = session.getServletContext().getRealPath("/kl.json");
}
Irrespective of passing cl=star in the url parameters, its not bringing any difference, and showing only kl.json
This code is in jsp, and as of now, no other framework is being used. It's being tested on Tom cat container.
NEVER compare strings using ==.
Always compare using the equals method.
request.getParameter("cl").equals("star")
Note that when using == to compare string objects, you are not comparing it's values but it's references.
Related
When the parameter *{mydata.value} is enum then how to transform it into String in thymeleaf?
I want to compare
if:*{mydata.value == "aaa"}
It gives error.
I think it is because I should do something like:
if:*{mydata.value.toString() == "aaa"}.
Try using
if:*{mydata.value.toString().equals("aaa")}
I'm not very familiar with thymeleaf, however that is a common issue in Java. Using '==' will compare the reference to the object, but the .equals() will compare the contents of the string.
If 'mydata.value' is already a string, you can remove the '.toString()'.
If it isn't a string already, you can also use:
if:*{String.valueOf(mydata.value).equals("aaa")}
See more examples of why this happens here
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 8 years ago.
my case:
I try to get a value from my MySQL database. This data is defined as a VARCHAR.
This is done in java with a prepared statement and resultset.
String add1 =rs.getString("include");
according to this website table 5.1 states "Can always be converted to these Java types".
therefore a VARCHAR should be able to be converted in a java.lang.string.
When i check the data type in java it indeed gives java.lang.string. So for so good.
My issue is when i try to compare this obtained "String" value to a in java defined String value they don't seem to be equal.
Let's give a simple example.
I get the (VARCHAR) value "1" from the database and store in in String add1
I want to check if this value is indeed "1" and therefore I use the following statement
if(add1=="1")
{
/* do something */
}
Only the values are , according to java, not the same. So I was curious about why this is.
I started searching why those two "Strings" are not equal.
First of I checked the length of both strings. Both came out to be 1 in length as expected.
Afterwards I checked the value of both. To see if both values where indeed the same i wanted to check their hexadecimal representance.
Both came out with the value 0x31. Still as expected.
But then why isn't my if statement accepted by java if both seem to represent the same string-hex-bin-you name it value.
In short: Why is my VARCHAR "String" obtained from a MySQL databse in java not the same as a String defined in java.
Compare values, not memory references:
if(add1.equals("1"))
{
/* do something */
}
Please see this post best answer.
You must always compare strings with the .equals method in your case it will be
add1.equals("1")
"==" or equality operator in Java is a binary operator It is good for compairing primitives like boolean, int, float "==" works fine but when it comes to compare objects it creates confusion with equals method in Java. "==" compare two objects based on memory reference. so "==" operator will return true only if two object reference it is comparing represent exactly same object otherwise "==" will return false.
String comparison is a common scenario of using both == and equals method. Since java.lang.String class override equals method, It return true if two String object contains same content but == will only return true if two references are pointing to same object.
Read more: http://javarevisited.blogspot.com/2012/12/difference-between-equals-method-and-equality-operator-java.html#ixzz3PdLbOre0
You need to compare the Strings with .equals() method. because == checks for object reference.
What is the difference between == vs equals() in Java?
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
If statement using == gives unexpected result
Hi I'm using this code to add elements to my ComboBox, and I do not want to add empty elements, here's the code:
public void elrendezesBetoltes(ArrayList<Elrendezes> ElrLista){
int i;
Elrendezes tmp;
model.removeAllElements();
model = new DefaultComboBoxModel(comboBoxItems);
for(i=0; i<ElrLista.size(); i++){
tmp = ElrLista.get(i);
if(tmp.getName()!="")comboBoxItems.add(tmp.getName()); //not working
addButton2(tmp.getSeatnum(),tmp.getCoord(),tmp.getFoglalt());
}
}
My problem is that the if statement is not working, it still adds empty names to my combobox. What am I doing wrong?
Always use equals method to compare Strings: -
if (tmp.getName()!="")
should be: -
if (!tmp.getName().equals(""))
or simply use this, if you want to check for empty string: -
if (!tmp.getName().isEmpty()) {
comboBoxItems.add(tmp.getName());
}
Use equals method to compare string. By using != operator, you are comparing the string instances, which is always going the be true as they(tmp.getName() and "") are not same string instances.
Change
tmp.getName()!=""
to
!"".equals(tmp.getName())
Putting "" as first string in comparison will take care of your null scenario as well i.e. it will not break if tmp.getName() is null.
Use equals():
if (!tmp.getName().equals(""))
Using == or != compares string references, not string contents. This is almost never what you want.
you have to compare Strings with "equals", then it will work
if(!tmp.getName().equals(""))comboBoxItems.add(tmp.getName())
you are comparing for identity (==, !=) but each String instance has its own identity, even when they are equal.
So you need to do !tmp.getName().equals("").
Generally it is considered best practice to start with the constant string first, because it will never be null: !"".equals(tmp.getName())
However, I would recommend to use apache commons lang StringUtils. It has a notEmpty() and notBlank() method that take care of null handling and also trimming.
PS: sometimes identity will work for Strings. but it should not be relied upon as it is caused by compiler or jvm optimization due to String immutability.
Use String#isEmpty()
if(!tmp.getName().isEmpty())
OR:
if(!tmp.getName().equals(""))
Always, check String equality with equals method. == operator only checks if two references point to the same String object.
Another alternative if not on Java 6 and isEmpty is unavailable is this:
if (tmp.getName.length()>0)
Checking for the length is supposed to be quicker than using .equals although tbh the potential gain is so small its not worth worrying too much about.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Java String.equals versus ==
I know it' a dumb question but why this code doesn't work.
boolean correct = "SampleText" == ((EditText)findViewById(R.id.editText1)).getText().toString();
if(correct) ((TextView)findViewById(R.id.textView1)).setText("correct!");
else ((TextView)findViewById(R.id.textView1)).setText("uncorrect!");
The point is to check if content of "editText1" is equal to "Sample Text"
In Java, two strings (and in general, two objects) must be compared using equals(), not ==. The == operator tests for identity (meaning: testing if two objects are exactly the same in memory), whereas the method equals() tests two objects for equality (meaning: testing if two objects have the same value), no matter if they're two different objects. Almost always you're interested in equality, not in identity.
To fix your code, do this:
String str = ((EditText)findViewById(R.id.editText1)).getText().toString();
boolean correct = "SampleText".equals(str);
Also notice that it's a good practice to put the string literal first in the call to equals(), in this way you're safe in case the second string is null, avoiding a possible NullPointerException.
In Java Strings have to be compared with their equals() method:
String foo = "foo";
String bar = "bar";
if (foo.equals(bar)) System.out.println("correct");
else System.out.println("incorrect");
to compare the values for two strings (for equality), you need to use equals, not == (or use equalsIgnoreCase if you do not care about case sensitivity).
Using equals will check the contents/values of the strings (as opposed to "==" which will only check if the two variables point to the same object - not the same value).
The correct way to compare 2 objects in java is using equals() method of Object class
And as String is an object in java, it should be compared in same way.
The correct way to compare a String is with,
s1.equals(s2)
So you can use this,
boolean correct = "SampleText".equals(((EditText)findViewById(R.id.editText1)).getText().toString());
((TextView)findViewById(R.id.textView1)).setText("SampleTest".equals(((EditText)findViewById(R.id.editText1)).getText().toString()) ? "correct!" : "incorrect!");
It's a bit long and theres probably a better way you could do this. The .toString() feels weird!
Hopefully this is an easy fix, but for the moment is is boggling me (Actionscript programmer new to Java programming).
I have a string variable coming from getExtra that I am comparing to a static sting in an if statement:
Bundle extras = getIntent().getExtras();
dir = extras.getString("com.activity.Dir");
Then I am utilizing this in an if statement
if (dir == "content"){
// load page content
} else {
// load a menu
}
I am Toasting the value of dir on the line before it and regardless of the value it will not hit the == statement; ie: if dir == "content", it hits the else; if dir == "foo", it hits the else, etc.
I tried placing dir into another String var and used .toString();
String directive = dir.toString();
That does the same thing. What am I missing here?
SOLVED: Used dir.equals("content");
// Thanks for you being patient with me SO!
You must not compare strings via ==, but via .equals()
Strings are Objects, and to do correct Object equality comparisions, you need to use
dir.equals("content");
or better yet (to avoid possible null pointer exceptions)
"content".equals(dir);
You should use equals for Strings on Java.
2 tips:
Add the string you know it isn't null to avoid nullpointers. Ex: "compare".equals(string)
Use equalsIgnoreCase() instead of equals if you wish to compare strings and ignore the case differences.
Use the equals method instead of ==
"vuqar"=="vuqar" or "vuqar"!="vuqar" not works correct
You have to use
if(vuqar.equals("vuqar")){//action}
OR
if(!"vuqar".equals("vuqar")){//action}