Local Variable Type Inference

Th local variable type inference is a feature released in Java 10, that enable to developers the possible to skip type declaration when implement local variables.

Code examples

The LocalVariableTypeInference.java class have some code examples to demonstrate the Java 10 capability to infer the local variable type.

    var list = new ArrayList<String>();  // infers ArrayList<String>

    var hashMap = new HashMap<String, String>();  // infers HashMap<String, String>

    var stringBuilder = new StringBuilder();  // infers StringBuilder()

Unit test

To ensure TypeInference from Java 10, the LocalVariableTypeInference.java class are fully reviewed by unit tests, that can be found in class HaversineAlgorithmTest.java.

Unit test example:

    @Test
    void localVariableTypeInferenceArrayList() {

        var optional = variableTypeInference.localVariableTypeInferenceArrayList();
        var someObject = optional.isPresent() ? optional.get() : Optional.empty();

        assertAll("localVariableTypeInference",
                () -> assertTrue(someObject instanceof ArrayList),
                () -> assertNotEquals(someObject, null)
        );
    }

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Run the code

Just open a terminal and paste the commands below:

    gradle clean build --stacktrace

For Intellij IDEA

    gradle clean build cleanidea idea --stacktrace

For Eclipse IDE

    gradle clean build cleaneclipse eclipse --stacktrace

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License

Copyright 2018, Juliano Macedo. See LICENSE file for details.

References

• JDK 10 Project
• JEP 286: Local-Variable Type Inference
• Style Guidelines for Local Variable Type Inference in Java