How to Check null in Java?

In Java, null is a literal. It is mainly used to assign a null value to a variable. A null value is possible for a string, object, or date and time, etc. We cannot assign a null value to the primitive data types such as int, float, etc.

In programming, usually we need to check whether an object or a string is null or not to perform some task on it. In order to check a null string, we have some predefined methods of string. Let’s take some examples of different data types to understand how we can check whether they are null or not.

String

In Java, String can be null, empty, or blank, and each one of them is distinct.

1. An empty string is a string object having some value, but its length is equal to zero. For example:

2. A blank string is a string that has whitespace as its value. Its length is always greater than 0 and neither empty nor null. For example:

3. A null string has no value and makes a string null by assigning a null keyword as a value to it. For example:

In order to check whether a String is null or not, we use the comparison operator(==). Let’s take an example of it to understand how we can use it for null checking.

NullCheckExample1.java

  // import required classes and packages  packagetutorAspire.javacodes;  // create class NullCheckExample1 class to check whether a string is empty or null  class NullCheckExample1 {  // main() method start  public static void main(String[] args) {      // create null, empty, and blank strings      String string1 = null;      String string2 = “”;      String string3 = ” “;      String string4 = “Test”;      // check whether string1 is null, empty, or blank  System.out.println(“string1 is ” + checkNullEmptyBlank(string1));      // check whether string2 is null, empty, or blank  System.out.println(“string2 is ” + checkNullEmptyBlank(string2));      // check whether string3 is null, empty, or blank  System.out.println(“string3 is ” + checkNullEmptyBlank(string3));      // check whether string4 is null, empty, or blank  System.out.println(“string4 is ” + checkNullEmptyBlank(string4));  }  // create checkNullEmptyBlank() method which check whether the string is empty, null or blank and return result to the main() method  public static String checkNullEmptyBlank(String strToCheck) {      // check whether the given string is null or not  if (strToCheck == null) {  return “NULL”;      }      // check whether the given string is empty or not  else if(strToCheck.isEmpty()) {  return “EMPTY”;      }      // check whether the given string is blank or not  else if(strToCheck.isBlank()) {  return “BLANK”;      }  else {  return “neither NULL, EMPTY nor BLANK”;      }  }  }  

Output:

How to Check null in Java

Date andDateTime object

Date and DateTime both are the non-primitive data types, so they can store a null value. Let’s take an example of a date and time object to understand how we can check a null date or datetime object.

NullCheckExample2.java

  //import required classes and packages   packagetutorAspire.javacodes;  importjava.text.ParseException;  importjava.text.SimpleDateFormat;  importjava.util.Date;  importjava.util.Scanner;  //create class NullCheckExample2 class to check whether the Date object is null or not  public class NullCheckExample2 {  // declare a variable of date type and initialize it with null  public static Date d1 = null;  public static Date finalResult;  // main() method start  public static void main(String args[])  {  // declare a variable of type string that will store the user-entered date in string format  String d2;    // create scanner class object  Scanner sc = new Scanner(System.in);    System.out.print(“Enter Date in dd/mm/yyyy format:”);          // take input from user and initialize variable       d2 = sc.nextLine();          // close scanner class obj  sc.close();      // create an instance of the SimpleDateFormat class for modifying the date object  SimpleDateFormatobj = new SimpleDateFormat(“dd/MM/yyyy”);        // use try-catch to parse string to date  try {    finalResult = obj.parse(d2);        } catch (ParseException e) {  // TODO Auto-generated catch block  e.printStackTrace();  }        // check whether date1 and date2 is null or not by using comparison operator  if(d1 == null) {  System.out.println(“Date d1 is NULL.”);      }    if(finalResult == null) {  System.out.println(“Date d2 is NULL.”);  }else {  System.out.println(“Date d2 is not NULL.”);      }  }  }  

Output:

How to Check null in Java

Java Object

In order to check whether a Java object is Null or not, we can either use the isNull() method of the Objects class or comparison operator. Let’s take an example to understand how we can use the isNull() method or comparison operator for null check of Java object.

NullCheckExample3.java

  // import required classes and packages  packagetutorAspire.javacodes;    // create NullCheckExample3 class to check whether Java object is null or not  public class NullCheckExample3 {    // main() method start  public static void main(String[] args) {    // create instance of User2  User2 userObj = new User2();    // get data of User2 by calling   User1 firstUser = userObj.getFirstUser();    // check whether firstUser is null or not  if (firstUser == null) {  System.out.println(“Object is Null”);          } else {  System.out.println(“Object is not Null”);                // set name for user1  firstUser.setName(“Paul”);  System.out.println(firstUser.getName());          }      }    }    // create User1 class having a name attribute  class User1 {    // declare name variable      String name;        // getter for getting name of User1  public String getName() {    // return name of User1  return name;      }        // setter for setting name of User1  public void setName(String name) {  this.name = name;      }  }  // create class User2 having variable of type User1  class User2 {        User1 obj;        // getter to get object of User1  public User1 getFirstUser() {  returnobj;      }  }  

Output:

How to Check null in Java

NullCheckExample4.java

  // import required classes and packages  packagetutorAspire.javacodes;    importjava.util.Objects;    // create NullCheckExample3 class to check whether Java object is null or not  public class NullCheckExample4 {    // main() method start  public static void main(String[] args) {    // create instance of User2  User2 userObj = new User2();    // get data of User2 by calling   User1 firstUser = userObj.getFirstUser();    // check whether firstUser is null or not  if (Objects.isNull(firstUser) ){  System.out.println(“Object is Null”);          } else {  System.out.println(“Object is not Null”);                // set name for user1  firstUser.setName(“Paul”);  System.out.println(firstUser.getName());          }      }    }    // create User1 class having a name attribute  class User1 {    // declare name variable      String name;        // getter for getting name of User1  public String getName() {    // return name of User1  return name;      }        // setter for setting name of User1  public void setName(String name) {  this.name = name;      }    }    // create class User2 having variable of type User1  class User2 {        User1 obj;        // getter to get object of User1  public User1 getFirstUser() {  returnobj;      }  }  

Output:

How to Check null in Java

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