Reports .equals() being called to compare a String with an empty string. It is normally more performant to test a String for emptiness by comparing its .length() to zero instead.

This means that when you have a code snippet like

someStringParam.equals("");

it can be replaced with

someStringParam.isEmpty();

However its opposite is also true that a string comparison like

"".equals(someStringParam);

can be replace with

someStringParam.isEmpty();

though there is no built-in inspection for that, at least not in the Community version of IntelliJ.

Template creation

You can start the creation using the predefined template called method calls:

$Instance$.$MethodCall$($Parameter$)

What I did to create the final search template is

• I replaced the $Instance$ variable with "",
• I replaced the $MethodCalls$ variable with the equals string explicitly,
• and renamed the $Parameter$ variable to $STRING_ARGUMENT$ to make it a bit more clear.

"".equals($STRING_ARGUMENT$)

The replacement part is also an easy one, we just want to call isEmpty() on $STRING_ARGUMENT$:

$STRING_ARGUMENT$.isEmpty()

String_Argument variable

There are multiple conditions this variable have to meet in order to make the template work.

The first one is that the variable have to have the type java.lang.String. You may remember the same thing from the There is no actual assertion called from AssertJ SoftAssertions post. If you don’t, please make sure that you read the Instance section of that post.

To apply the condition we need to add a Type filter to this variable with the following value:

java\.lang\.String

However there is one more thing that is also worth adding. It doesn’t make sense to compare string literals to "", thus the text constraint of this variable needs to be configured as well to not match against literals, only variables.

First you need to create a regexp for string literals (values starting and ending with the " character). I assembled the one below:

^".*"$

But leaving the configuration in its current state would match calls to equals like

"".equals("")
"".equals("someStringValue")

therefore we need to negate the regexp by adding an ! at the beginning of it. This will tell IntelliJ to look for occurrences that is not like the regexp specified.

Finalization

In its final form this template will only match calls like

"".equals(someString)

where someString is an instance of java.util.String.

The XML representation of the inspection can be found in the summary document in the related GitHub repository.

See assets on GitHub.

Obviously there are other examples of this rule, so I’m going to explain the creation of a template to replace the usages of com.google.common.base.Preconditions.checkNotNull to java.util.Objects.requireNonNull.

Template creation

In case of this template I started with the predefined template called method calls:

$Instance$.$MethodCall$($Parameter$)

Then I renamed the variables and replaced the $Instance$ variable with the explicit reference of the Guava Preconditions class:

com.google.common.base.Preconditions.$CHECK_METHOD$($ARGUMENTS$)

In the replacement template you can use the same variables as you defined in the search template section, but only those. If you use a variable in the replacement section that is not defined in the search template you get the following popup message pointing to the specific variable:
Malformed replacement pattern Replacement variable is not defined.

In this template the $ARGUMENTS$ variable remains unchanged, and since we should use the native Java based solution, I replaced the $CHECK_METHOD$ variable to the explicitly defined java.util.Objects.requireNonNull.

java.util.Objects.requireNonNull($ARGUMENTS$);

Check_Method variable

The only thing that is crucial in case of this variable is the name of the method we are searching for, which is checkNotNull, therefore you need to add a Text filter with

checkNotNull

or you may want to use

^checkNotNull$

Arguments variable

While Preconditions.checkNotNull() has multiple signatures with different parameter lists, Objects.requireNonNull() doesn’t have matching method signatures for all of them. Therefore in this template I decided not to add a Count filer, thus searching only for the method with only one parameter.

Of course after this tutorial you will be able to easily create Replace templates for the matching method pairs.

Finalization

This template finds usages of the checkNotNull method both as a statement

and in assignments as well:

The XML representation of the inspection can be found in the summary document in the related GitHub repository.

See assets on GitHub.