This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 9 years ago.
I can't seem to get the code within the second if statement to execute. I have logged both values being compared and also ran the debugger and checked them. They are both "a". It always shows the incorrectPasswordDialog. This question seems difficult because it seems as though it should just work but any help is appreciated.
private void logUserIn(AppUser user) {
if (user != null){
Log.d("mPassword: ", mPassword);
Log.d("user.getPassword(): ", user.getPassword());
String userPassword = user.getPassword().toString();
String formPassword = mPassword.toString();
if ( userPassword == formPassword ){
Intent welcomePage = new Intent(this, StartScreenActivity.class);
welcomePage.putExtra("name", mName);
startActivity(welcomePage);
}
else {
showIncorrectPasswordDialog();
}
}else {
showIncorrectUserNameDialog();
}
}
You are comparing the object identity. Use string.equals() to check for equivalence.
if(userPassword.equals(formPassword)){
}
Change
if ( userPassword == formPassword ){
to
if ( userPassword.equals(formPassword) ){
== compares object references, whereas .equals compared String values.
You can not compare string using ==
try like this
Compares the specified object to this string and returns true if they are equal. The object must be an instance of string with the same characters in the same order.
if ( userPassword.equals(formPassword)){
// do some stuff
}
or
Compares the specified string to this string ignoring the case of the characters and returns true if they are equal.
if(userPassword.equalsIgnoreCase(formPassword))
{
//do some stuff
}
In JAVA to compare between strings, you should use:
if(userPassword.equals(formPassword)) {
// they are equal
}
Change
if ( userPassword == formPassword ){
to
if ( userPassword.equals(formPassword)){
In Java, String comparison is done with .equals(). Using == compares the object reference and not their values.
Java String comparison
In JAVA you should use equals to judge equal of value of different String.
== is used to judge object pointer for string, so it would only return false in your case.
Related
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 4 years ago.
I have the following piece of code:
String week = this.getIntent().getStringExtra("weekNumber");
String correctWeek = Integer.toString(Calendar.WEEK_OF_YEAR);
if (week == correctWeek) {
correct();
}
else incorrect();
They are both "3", but the comparation result is false and I don't know why:
Where is the error?
Use equals() to compare strings for content, not ==.
== will check if the objects are the same.
String foo = "foo";
if (foo == foo) {
// same object, so true
}
String foo1 = "foo";
String foo2 = "foo";
if (foo1 == foo2) {
// both are string literals set at compile time, so true
}
String foo1 = loadFoo1(); // imagine this returns "foo"
String foo2 = loadFoo2(); // imagine this also returns "foo"
if (foo1 == foo2) {
// not the same object, and not string literals, so false
}
if (foo1.equals(foo2)) {
// both strings hold "foo", so true
}
The two strings are separate objects, and "==" tests if its two operands are the same exact object.
To compare strings, try week.equals(correctWeek)
The "==" operator is used for reference comparison. It checks if both objects point to the same memory location, which returns false in your case as you are comparing two different string objects.
For your purpose you should use .equals(), which evaluates to the comparison of values in the objects.
Example:
String week = new String("3");
String correctWeek = new String("3");
System.out.println(week == correctWeek);
System.out.println(week.equals(correctWeek));
will output:
false
true
hi i'm wonder why my if always Toast me : "names Successfully saved!"
i'm try every thing.
public void btnSave_Clicked(View view) {
TextView txtOname = (TextView)findViewById(R.id.txtOname);
TextView txtXname = (TextView)findViewById(R.id.txtXname);
String X = txtXname.getText().toString();
String O = txtOname.getText().toString();
if((X!="") && (O!="")){
DatabaseHelper.insertName(getBaseContext(),((TextView)findViewById(R.id.txtOname))
.getText().toString());
DatabaseHelper.insertName(getBaseContext(),((TextView)findViewById(R.id.txtXname))
.getText().toString());
Toast.makeText(this,"names Successfully saved!",Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(this,"E",Toast.LENGTH_SHORT).show();
}
}
}
Strings are reference types in Java, and thus the reference of a dynamically created empty string will be different from your variables. Another option to isEmpty is equals.
if (!x.equals("") && !o.equals(")) {
//code
}
Though I'd probably go with isEmpty
Replace your if statement with:
if (!x.isEmpty() && !o.isEmpty()) {
//code
}
operator == compares Object reference.
.equals() compares String value.
.isEmpty() return true if String length is 0.
Strings are objects. Object instances (the value behind them) have to be compared manually with a method to assure that the content is the same.
The == operator just compares the string references ("adresses"). So when you create 2 object instances at runtime, they have different adresses even if the content is the same. Compile-time strings on the other hand are internalized, they are put into special memory and duplicates are sorted out.
System.out.println(new String("test") == new String("test"));
This will print false, because those 2 objects get created at runtime. The new keyword in the first example mandates that a new object with a new adress is created.
System.out.println("test" == "test");
This will print true, because they are String literals, which are known at runtime, you are not explicitly stating the new keyword here either. You are simply specifying that you want those literals represented in the code somehow, so the compiler internalizes them.
This question already has answers here:
Check whether a String is not Null and not Empty
(35 answers)
Closed 6 years ago.
May occur any exception in coding for checking string is null or not ? Please help.
String code ;
if (!code.equals(null)) {
}
else
{
}
Here is how you can check if String value is null or not
if(code != null){
}else{
}
You can not us !code.equals(null) because, equals is used to compare same object type. null is not any object type and code is String. If you consider null as String, then you can use !code.equals("null")
String can be checked like this:
if(code.equals("null") || code.equals("")) {
// code to do when string is null.
}
else {
// code to do when string is not null.
}
equals() is use to check the similarity of two String, and == or != is use to check the condition. In your case you are checking the similarity of string.
if (!code.equals(null)) {
//code checks that String code is equal to null or not
}
else
{
}
another
if (code != null) {
//code checks if code is not equals to null (condition checking)
}
else
{
}
There are many ways to check if String is empty in Java, but what is the right way of doing it? right in the sense of robustness, performance and readability. If robustness is your priority then using equals() method or Apache commons StringUtils is the right way to do this check. If you don't want to use third party library and happy of doing null check by yourself, then checking String's length is the fastest way and using isEmpty() method from String is most readable way. By the way, don't confuse between empty and null String, if your application treat them same, then you can consider them same otherwise they are different, as null may not be classified as empty. Here are three examples of checking String is empty or not by using JDK library itself.
Read more Here
You can't use .equals(null) to make a null check, because the API description for Object#equals states that:
For any non-null reference value x, x.equals(null) should return false.
Not only would this be a useless check (since it always returns false), it would also throw a NullPointerException if code actually was null, because a null value does not define an equals method.
Object x = null;
boolean isNull = x.equals(null); // NullPointerException on .equals
The only practical way to do a null check is to use:
if (code != null) {
}
If you want to check whether string is empty i.e. null or "" then use
if(TextUtils.isEmpty(code)){
}else{
}
equals checks the value exists in string.
I am trying to check user's inserted password with saved password in the database.
This is my methode:
private Boolean CheckPassword()
{
TextView txt_pass = (TextView) findViewById(R.id.login_password_txt);
String _writtenPassword = txt_pass.getText().toString().trim();
if (_writtenPassword == userPassword)
return true;
Log.d(TAG, userPassword);
Log.d(TAG, _writtenPassword);
Log.d(TAG, String.valueOf(userPassword.length()));
Log.d(TAG, String.valueOf(_writtenPassword.length()));
return false;
}
The log shows me the password and length.
The result is:
123
123
3
3
But this methode returns False!!!
Can anyone help me please?
Try this..
String you should compares with .equals("")
if (_writtenPassword.equals(userPassword))
return true;
== always just compares two references
Refer this String comparison
Use the if-else control structure and also use the equals() for comparing two strings like this,
if (_writtenPassword.equals(userPassword))
return true;
else
return false;
Alternatively you can use matches
if (_writtenPassword.matches(userPassword))
return true;
///your code
expression _writtenPassword == userPassword is true whenever reference of _writtenPassword and userPassword are same.
Since you don't care about their reference but you care about their value so use expression
_writtenPassword.equals(userPassword)which is true whenever the value of_writtenPasswordanduserPassword` are same.
Try this:
return _writtenPassword.equals(userPassword);
I've a string value String str="Success"
How to check the "str" value is not equal to "Success". If I try if(str!="Success"). It is not working properly.
I've a integer value int a=250 If I use If(a!=250) this is also not working properly.
How to code for these conditional statements ? I'm using Android and Eclipse version 2.1.
Any help would be appreciable.
a!=250 should work.
For string try str.equals("Success")
As every one said, String values should compare with .equals method.
like
if(str.equals("Success"))
{
System.out.println("My String is Success");
}
Next coming to integer comparison.
As you have said, you have the integer value
int a=250
if(a!=250)
{
// Some code
}
Here already your a value is 250. then you are executing some lines of code if a value is not equal to 250. Then how the condition will execute. if you want to test then
change the a value and then check again as
int a=50
if(a!=250)
{
// Some code===============> Now this code will execute
}
For string comparison, use the standard String.equals() method.
str.equals("Success"); - For Equals
if(!str.equals("Success")) - For Not Equals(your case)
And for int, what is being used, is proper. a!=250 will return false in your case. Hence, it'll not enter the if block.
You should try to study Java first ;)
This is not the way to do a String comparison. For String comparison, you must use .equals(String) method.
String str1 = "str1";
String str2 = "str2";
if(str1.equals(str2)) {
//do something
}
You should not compare strings with != or =. That won't work in most cases.
new String("test").equals("test")
Should be used for comparison.
!= compares the value and is true if they are NOT equal.
you could also use something like if(a == 250){...}
In Java you cannot use == to compare Strings, you must use:
if(string.equals("example"))
So let's use equals() in your conditional and optimize it:
if(!str.equals("Success"))
this will work