public boolean isValidCardDetails(CardDetailsTypeBean cardDetailsTypeBean) throws EnrollmentReqInvalidException {
if (cardDetailsTypeBean.getCardNumber() == null || "".equals(cardDetailsTypeBean.getCardNumber())) {
throw new EnrollmentReqInvalidException("ECDOO16", "card no is mandatory");
}
if (cardDetailsTypeBean.getNameOnCard() == null || "".equals(cardDetailsTypeBean.getNameOnCard())) {
throw new EnrollmentReqInvalidException("ECDOO17", "name on card is mandatory");
}
if (cardDetailsTypeBean.getCvv() == 0 || "".equals(String.valueOf(cardDetailsTypeBean.getCvv()))) {
throw new EnrollmentReqInvalidException("ECDOO18", "cvv is mandatory");
}
if (cardDetailsTypeBean.getExpDate() == null || "".equals(cardDetailsTypeBean.getExpDate())) {
throw new EnrollmentReqInvalidException("ECDOO19", "exp date must be required");
}
return false;
}
Well here i want to ask after getting card number and checking null,why we use "".equals there..?? can anyone explain me this? little confused?
This line of code:
cardDetailsTypeBean.getCardNumber() == null || "".equals(cardDetailsTypeBean.getCardNumber())
simply verifies if cardNumber is null or if is equal to the empty string. Empty string is different from null value, so this code checks if every field read by a getter returns a non-empty, non-null value.
It's superfluous, actually.
The reason for this is that the order of the equals statement on the other side of the logical comparison is guaranteed not to produce a NullPointerException, since String.equals(null) is engineered to produce false.
The reason it likely exists the way it does is that it's being made explicit that the code is checking for null and an empty string.
"" isn't the same as null because "" is a String value. Your card number might instantiated with ""
null means the reference of card number has no value.
How can I check whether a string is not null and not empty?
public void doStuff(String str)
{
if (str != null && str != "**here I want to check the 'str' is empty or not**")
{
/* handle empty string */
}
/* ... */
}
What about isEmpty() ?
if(str != null && !str.isEmpty())
Be sure to use the parts of && in this order, because java will not proceed to evaluate the second part if the first part of && fails, thus ensuring you will not get a null pointer exception from str.isEmpty() if str is null.
Beware, it's only available since Java SE 1.6. You have to check str.length() == 0 on previous versions.
To ignore whitespace as well:
if(str != null && !str.trim().isEmpty())
(since Java 11 str.trim().isEmpty() can be reduced to str.isBlank() which will also test for other Unicode white spaces)
Wrapped in a handy function:
public static boolean empty( final String s ) {
// Null-safe, short-circuit evaluation.
return s == null || s.trim().isEmpty();
}
Becomes:
if( !empty( str ) )
Use org.apache.commons.lang.StringUtils
I like to use Apache commons-lang for these kinds of things, and especially the StringUtils utility class:
import org.apache.commons.lang.StringUtils;
if (StringUtils.isNotBlank(str)) {
...
}
if (StringUtils.isBlank(str)) {
...
}
Just adding Android in here:
import android.text.TextUtils;
if (!TextUtils.isEmpty(str)) {
...
}
To add to #BJorn and #SeanPatrickFloyd The Guava way to do this is:
Strings.nullToEmpty(str).isEmpty();
// or
Strings.isNullOrEmpty(str);
Commons Lang is more readable at times but I have been slowly relying more on Guava plus sometimes Commons Lang is confusing when it comes to isBlank() (as in what is whitespace or not).
Guava's version of Commons Lang isBlank would be:
Strings.nullToEmpty(str).trim().isEmpty()
I will say code that doesn't allow "" (empty) AND null is suspicious and potentially buggy in that it probably doesn't handle all cases where is not allowing null makes sense (although for SQL I can understand as SQL/HQL is weird about '').
str != null && str.length() != 0
alternatively
str != null && !str.equals("")
or
str != null && !"".equals(str)
Note: The second check (first and second alternatives) assumes str is not null. It's ok only because the first check is doing that (and Java doesn't does the second check if the first is false)!
IMPORTANT: DON'T use == for string equality. == checks the pointer is equal, not the value. Two strings can be in different memory addresses (two instances) but have the same value!
Almost every library I know defines a utility class called StringUtils, StringUtil or StringHelper, and they usually include the method you are looking for.
My personal favorite is Apache Commons / Lang, where in the StringUtils class, you get both the
StringUtils.isEmpty(String) and the
StringUtils.isBlank(String) method
(The first checks whether a string is null or empty, the second checks whether it is null, empty or whitespace only)
There are similar utility classes in Spring, Wicket and lots of other libs. If you don't use external libraries, you might want to introduce a StringUtils class in your own project.
Update: many years have passed, and these days I'd recommend using Guava's Strings.isNullOrEmpty(string) method.
This works for me:
import com.google.common.base.Strings;
if (!Strings.isNullOrEmpty(myString)) {
return myString;
}
Returns true if the given string is null or is the empty string.
Consider normalizing your string references with nullToEmpty. If you
do, you can use String.isEmpty() instead of this method, and you won't
need special null-safe forms of methods like String.toUpperCase
either. Or, if you'd like to normalize "in the other direction,"
converting empty strings to null, you can use emptyToNull.
There is a new method in java-11: String#isBlank
Returns true if the string is empty or contains only white space codepoints, otherwise false.
jshell> "".isBlank()
$7 ==> true
jshell> " ".isBlank()
$8 ==> true
jshell> " ! ".isBlank()
$9 ==> false
This could be combined with Optional to check if string is null or empty
boolean isNullOrEmpty = Optional.ofNullable(str).map(String::isBlank).orElse(true);
String#isBlank
How about:
if(str!= null && str.length() != 0 )
Returns true or false based on input
Predicate<String> p = (s)-> ( s != null && !s.isEmpty());
p.test(string);
Use Apache StringUtils' isNotBlank method like
StringUtils.isNotBlank(str)
It will return true only if the str is not null and is not empty.
For completeness: If you are already using the Spring framework, the StringUtils provide the method
org.springframework.util.StringUtils.hasLength(String str)
Returns:
true if the String is not null and has length
as well as the method
org.springframework.util.StringUtils.hasText(String str)
Returns:
true if the String is not null, its length is greater than 0, and it does not contain whitespace only
You can use the functional style of checking:
Optional.ofNullable(str)
.filter(s -> !(s.trim().isEmpty()))
.ifPresent(result -> {
// your query setup goes here
});
You should use org.apache.commons.lang3.StringUtils.isNotBlank() or org.apache.commons.lang3.StringUtils.isNotEmpty. The decision between these two is based on what you actually want to check for.
The isNotBlank() checks that the input parameter is:
not Null,
not the empty string ("")
not a sequence of whitespace characters (" ")
The isNotEmpty() checks only that the input parameter is
not null
not the Empty String ("")
If you don't want to include the whole library; just include the code you want from it. You'll have to maintain it yourself; but it's a pretty straight forward function. Here it is copied from commons.apache.org
/**
* <p>Checks if a String is whitespace, empty ("") or null.</p>
*
* <pre>
* StringUtils.isBlank(null) = true
* StringUtils.isBlank("") = true
* StringUtils.isBlank(" ") = true
* StringUtils.isBlank("bob") = false
* StringUtils.isBlank(" bob ") = false
* </pre>
*
* #param str the String to check, may be null
* #return <code>true</code> if the String is null, empty or whitespace
* #since 2.0
*/
public static boolean isBlank(String str) {
int strLen;
if (str == null || (strLen = str.length()) == 0) {
return true;
}
for (int i = 0; i < strLen; i++) {
if ((Character.isWhitespace(str.charAt(i)) == false)) {
return false;
}
}
return true;
}
test equals with an empty string and null in the same conditional:
if(!"".equals(str) && str != null) {
// do stuff.
}
Does not throws NullPointerException if str is null, since Object.equals() returns false if arg is null.
the other construct str.equals("") would throw the dreaded NullPointerException. Some might consider bad form using a String literal as the object upon wich equals() is called but it does the job.
Also check this answer: https://stackoverflow.com/a/531825/1532705
Simple solution :
private boolean stringNotEmptyOrNull(String st) {
return st != null && !st.isEmpty();
}
As seanizer said above, Apache StringUtils is fantastic for this, if you were to include guava you should do the following;
public List<Employee> findEmployees(String str, int dep) {
Preconditions.checkState(StringUtils.isNotBlank(str), "Invalid input, input is blank or null");
/** code here **/
}
May I also recommend that you refer to the columns in your result set by name rather than by index, this will make your code much easier to maintain.
You can use StringUtils.isEmpty(), It will result true if the string is either null or empty.
String str1 = "";
String str2 = null;
if(StringUtils.isEmpty(str)){
System.out.println("str1 is null or empty");
}
if(StringUtils.isEmpty(str2)){
System.out.println("str2 is null or empty");
}
will result in
str1 is null or empty
str2 is null or empty
I've made my own utility function to check several strings at once, rather than having an if statement full of if(str != null && !str.isEmpty && str2 != null && !str2.isEmpty). This is the function:
public class StringUtils{
public static boolean areSet(String... strings)
{
for(String s : strings)
if(s == null || s.isEmpty)
return false;
return true;
}
}
so I can simply write:
if(!StringUtils.areSet(firstName,lastName,address)
{
//do something
}
In case you are using Java 8 and want to have a more Functional Programming approach, you can define a Function that manages the control and then you can reuse it and apply() whenever is needed.
Coming to practice, you can define the Function as
Function<String, Boolean> isNotEmpty = s -> s != null && !"".equals(s)
Then, you can use it by simply calling the apply() method as:
String emptyString = "";
isNotEmpty.apply(emptyString); // this will return false
String notEmptyString = "StackOverflow";
isNotEmpty.apply(notEmptyString); // this will return true
If you prefer, you can define a Function that checks if the String is empty and then negate it with !.
In this case, the Function will look like as :
Function<String, Boolean> isEmpty = s -> s == null || "".equals(s)
Then, you can use it by simply calling the apply() method as:
String emptyString = "";
!isEmpty.apply(emptyString); // this will return false
String notEmptyString = "StackOverflow";
!isEmpty.apply(notEmptyString); // this will return true
If you are using Spring Boot then below code will do the Job
StringUtils.hasLength(str)
With Java 8 Optional you can do:
public Boolean isStringCorrect(String str) {
return Optional.ofNullable(str)
.map(String::trim)
.map(string -> !str.isEmpty())
.orElse(false);
}
In this expression, you will handle Strings that consist of spaces as well.
To check if a string is not empty you can check if it is null but this doesn't account for a string with whitespace. You could use str.trim() to trim all the whitespace and then chain .isEmpty() to ensure that the result is not empty.
if(str != null && !str.trim().isEmpty()) { /* do your stuffs here */ }
I would advise Guava or Apache Commons according to your actual need. Check the different behaviors in my example code:
import com.google.common.base.Strings;
import org.apache.commons.lang.StringUtils;
/**
* Created by hu0983 on 2016.01.13..
*/
public class StringNotEmptyTesting {
public static void main(String[] args){
String a = " ";
String b = "";
String c=null;
System.out.println("Apache:");
if(!StringUtils.isNotBlank(a)){
System.out.println(" a is blank");
}
if(!StringUtils.isNotBlank(b)){
System.out.println(" b is blank");
}
if(!StringUtils.isNotBlank(c)){
System.out.println(" c is blank");
}
System.out.println("Google:");
if(Strings.isNullOrEmpty(Strings.emptyToNull(a))){
System.out.println(" a is NullOrEmpty");
}
if(Strings.isNullOrEmpty(b)){
System.out.println(" b is NullOrEmpty");
}
if(Strings.isNullOrEmpty(c)){
System.out.println(" c is NullOrEmpty");
}
}
}
Result:
Apache:
a is blank
b is blank
c is blank
Google:
b is NullOrEmpty
c is NullOrEmpty
Simply, to ignore white space as well:
if (str == null || str.trim().length() == 0) {
// str is empty
} else {
// str is not empty
}
Consider the below example, I have added 4 test cases in main method. three test cases will pass when you follow above commented snipts.
public class EmptyNullBlankWithNull {
public static boolean nullEmptyBlankWithNull(String passedStr) {
if (passedStr != null && !passedStr.trim().isEmpty() && !passedStr.trim().equals("null")) {
// TODO when string is null , Empty, Blank
return true;
}else{
// TODO when string is null , Empty, Blank
return false;
}
}
public static void main(String[] args) {
String stringNull = null; // test case 1
String stringEmpty = ""; // test case 2
String stringWhiteSpace = " "; // test case 3
String stringWhiteSpaceWithNull = " null"; // test case 4
System.out.println("TestCase result:------ "+nullEmptyBlankWithNull(stringWhiteSpaceWithNull));
}
}
BUT test case 4 will return true(it has white space before null) which is wrong:
String stringWhiteSpaceWithNull = " null"; // test case 4
We have to add below conditions to make it work propper:
!passedStr.trim().equals("null")
If you use Spring framework then you can use method:
org.springframework.util.StringUtils.isEmpty(#Nullable Object str);
This method accepts any Object as an argument, comparing it to null and the empty String. As a consequence, this method will never return true for a non-null non-String object.
To check on if all the string attributes in an object is empty(Instead of using !=null on all the field names following java reflection api approach
private String name1;
private String name2;
private String name3;
public boolean isEmpty() {
for (Field field : this.getClass().getDeclaredFields()) {
try {
field.setAccessible(true);
if (field.get(this) != null) {
return false;
}
} catch (Exception e) {
System.out.println("Exception occurred in processing");
}
}
return true;
}
This method would return true if all the String field values are blank,It would return false if any one values is present in the String attributes
I've encountered a situation where I must check that "null" (as a string) must be regarded as empty. Also white space and an actual null must return true.
I've finally settled on the following function...
public boolean isEmpty(String testString) {
return ((null==testString) || "".equals((""+testString).trim()) || "null".equals((""+testString).toLowerCase()));
}
this is my first so I'll try to add as much info as possible so I don't get yelled at. :-)
What I am trying to do is I have 2 variables that grab text from 2 fields and take only the first character from each and assign it to those values.
This is the code that I use to get the strings. They are 2 separate calls as you would.
try { var_ContactSurname = var_ContactSurname.substring(0,1);
}
catch (Exception e){
}
I have the above again with a different variable. Now to this point it does what I want. It grabs the first letter from the fields and assigns it to the variables.
So at this point I have two variables (say with an example charater of D and R).
var_ContactSurname = R
var_ContactLicenceNumber = D
What I want to do is compare those two variables and if they match I want to return a value of TRUE, else FALSE if they don't match.
That value has to be a string as well and be assigned to a new variable called var_ContactValidate.
if (var_ContactLicenceNumber.toLowerCase().equals()var_ContactSurname.toLowerCase()){
var_ContactValidate == "TRUE";
}
else {
var_ContactValidate == "FALSE";
}
No you may notice that there might be some code missing. I am using a rules engine that does a lot of the functions for me. I can use raw Java code to do other things (like this compare)...but that's the compare that I am having a problem with.
Any ideas for that compare would be greatly appreciated.
Thanks.
i would use the String method equalsIgnoreCase()
to assign a value to a field, use a single =, not double (==).
if (var_ContactLicenceNumber.equalsIgnoreCase(var_ContactSurname){
var_ContactValidate = "TRUE";
}
else {
var_ContactValidate = "FALSE";
}
check it
In addition to what already said - a simpler & more elegant version (without the if condition) could be:
var_ContactValidate = Boolean.toString(
var_ContactLicenceNumber.equalsIgnoreCase(var_ContactSurname))
.toUpperCase();
Change your whole piece of code to:
if (var_ContactLicenceNumber.equalsIgnoreCase(var_ContactSurname)){
var_ContactValidate == "TRUE";
}
else {
var_ContactValidate == "FALSE";
}
This combines the case insensitivity that you want, and passes through the second string as an argument of the .equalsIgnoreCase function.
Also, I am not sure what you are trying to do with the line:
var_ContactValidate == "TRUE";
If you want to assign var_ContactValidate to "TRUE" then use a single equals sign '=' as a double equals '==' compares the values instead. You may also considering using a boolean rather than a string in this case.
Here is an implementation that also checks for null values and empty Strings:
public class SurnameAndLicenseValidator {
public static void main(String[] args) {
// FALSE
validateSurnameAndLicense(null, "jb78hq");
validateSurnameAndLicense("Johnson", null);
validateSurnameAndLicense(null, null);
validateSurnameAndLicense("", "jb78hq");
validateSurnameAndLicense("Johnson", "");
validateSurnameAndLicense("", "");
validateSurnameAndLicense("johnson", "xb78hq");
// TRUE
validateSurnameAndLicense("Johnson", "jb78hq");
validateSurnameAndLicense("johnson", "jb78hq");
}
private static String validateSurnameAndLicense(String surname,
String license) {
String result;
if (surname != null
&& surname.length() > 0
&& license != null
&& license.length() > 0
&& Character.toUpperCase(surname.charAt(0)) == Character
.toUpperCase(license.charAt(0))) {
result = "TRUE";
} else {
result = "FALSE";
}
System.out.println(surname + " " + license + " " + result);
return result;
}
}
The main method is used as a unit test here. You might want to extract a real JUnit test from it, if you are into that kind of thing.
I'm trying to check if a form field is empty in java. I search a lot, But I only found it in javascript.
The problem is I want to check it in my Controller.
How can I do this?
Regards.
Thank you.
You can check parameter by HttpServletRequest :
String p = req.getParameter("p");
if(p==null){
System.out.println("parameter p is empty");
}
If you are testing it in your controller:
if(request.getParameter().trim().compareTo("") == 0){ // Do what you want
If you are testing it in your page, simply try this:
if(field.text.toString().trim().compareTo("") == 0){ //Do what you want
With Java 6 you can test an empty String :
if(null == myString || myString.trim().isEmpty() { .. ;}
EDIT to add trim() for blank removing
Checking empty filed you have to check null and empty string.
if(str == null && str.equals(""){}
if(string.equals(""))
{
}
How to check if the string is not null?
if(!string.equals(""))
{
}
Checking for null is done via if (string != null)
If you want to check if its null or empty - you'd need if (string != null && !string.isEmpty())
I prefer to use commons-lang StringUtils.isNotEmpty(..)
You can do it with the following code:
if (string != null) {
}
Checking for null is done by:
string != null
Your example is actually checking for the empty string
You can combine the two like this:
if (string != null && !string.equals("")) { ...
But null and empty are two different things
Nothing really new to add to the answers above, just wrapping it into a simple class. Commons-lang is quite all right but if all you need are these or maybe a few more helper functions, rolling your own simple class is the easiest approach, also keeping executable size down.
public class StringUtils {
public static boolean isEmpty(String s) {
return (s == null || s.isEmpty());
}
public static boolean isNotEmpty(String s) {
return !isEmpty(s);
}
}
Use TextUtils Method.
TextUtils.isEmpty(str) : Returns true if the string is null or 0-length. Parameters: str the string to be examined Returns: true if str is null or zero length
if(TextUtils.isEmpty(str)){
// str is null or lenght is 0
}
Source of TextUtils class
isEmpty Method :
public static boolean isEmpty(CharSequence str) {
if (str == null || str.length() == 0)
return true;
else
return false;
}
if(str != null && !str.isEmpty())
Be sure to use the parts of && in this order, because java will not proceed to evaluating the the second if the first part of && fails, thus ensuring you will not get a null pointer exception from str.isEmpty() if str is null.
Beware, it's only available since Java SE 1.6.
You have to check str.length() == 0 or str.equals("")
on previous versions.
As everyone is saying, you'd have to check (string!=null), in objects you're testing the memory pointer.
because every object is identified by a memory pointer, you have to check your object for a null pointer before testing anything else, so:
(string!=null && !string.equals("")) is good
(!string.equals("") && string !=null) can give you a nullpointerexception.
if you don't care for trailing spaces you can always use trim() before equals()
so " " and "" gives you the same result
The best way to check a String is :
import org.apache.commons.lang3.StringUtils;
if(StringUtils.isNotBlank(string)){
....
}
From the doc :
isBlank(CharSequence cs) :
Checks if a CharSequence is empty (""), null
or whitespace only.
You can use Predicate and its new method (since java 11) Predicate::not
You can write code to check if string is not null and not empty:
Predicate<String> notNull = Predicate.not(Objects::isNull);
Predicate<String> notEmptyString = Predicate.not(String::isEmpty);
Predicate<String> isNotEmpty = notNull.and(notEmptyString);
Then you can test it:
System.out.println(isNotEmpty.test("")); // false
System.out.println(isNotEmpty.test(null)); // false
System.out.println(isNotEmpty.test("null")); // true
A common way for testing null string in Java is with Optionals:
Optional.ofNullable(myString).orElse("value was null")
Optional.ofNullable(myString).ifPresent(s -> System.out.println(s));
Optional.ofNullable(myString).orElseThrow(() -> new RuntimeException("value was null"));
And to test if it is null or empty you can use Apache org.apache.commons.lang3 library that gives you the following methods:
StringUtils.isEmpty(String) / StringUtils.isNotEmpty(String): It tests if the String is null or empty (" " is not empty)
StringUtils.isBlank(String) / StringUtils.isNotBlank(String): Same as isEmpty bt if the String is only whitespace it is considered blank
And applied to Optional you get:
Optional.ofNullable(myString).filter(StringUtils::isNotEmpty).orElse("value was null or empty");
Try using Strings.isNullOrEmpty("") from com.google.common.base.Strings this method returns boolean value and checks for both null and empty string.
if(string != null)
or
if(string.length() == 0)
or
if(("").equals(string))
u can try this
if(string != null)