How to Check Null in Java

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Last Updated: March 21, 2023 Tested

Using an If Statement

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Using a Null Check

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Tips

A null indicates that a variable doesn't point to any object and holds no value. You can use a basic ‘if’ statement to check a null in a piece of code. Null is commonly used to denote or verify the non-existence of something. Within that context, it can be used as a condition to start or stop other processes within the code.^{[1]
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Part 1

Part 1 of 2:

Using an If Statement

1
Use “=” to define a variable. A single “=” is used to declare a variable and assign a value to it. You can use this to set a variable to null.
- A value of “0” and null are not the same and will behave differently.
- variableName = null;
2
Use “==” to check a variable’s value. A “==” is used to check that the two values on either side are equal. If you set a variable to null with “=” then checking that the variable is equal to null would return true.
- variableName == null;
- You can also use “!=” to check that a value is NOT equal.
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3
Use an “if” statement to create a condition for the null. The result of the expression will be a boolean (true or false) value. You can use the boolean value as a condition for what the statement does next.
- For example, if the value is null, then print text “object is null”. If “==” does not find the variable to be null, then it will skip the condition or can take a different path.
  Object object = null ; if ( object == null ) { System.out.print ( "object is null "); }

Part 2

Part 2 of 2:

Using a Null Check

1
Use null as an unknown value. It is common to use null as a default in lieu of any assigned value.
- string() means the value is null until it is actually used.
2
Use null as a condition for ending a process. Returning a null value can be used to trigger the end of a loop or break a process. This is more commonly used to throw an error or exception when something has gone wrong or an undesired condition has been hit.
3
Use null to indicate an uninitiated state. Similarly, null can be used as flag to show that a process has not yet started or as a condition to mark to be beginning of a process.
- For example: do something while object is null or do nothing until an object is NOT null.
  synchronized method() { while (method()==null); method().nowCanDoStuff(); }