Optional in Java 1.7? Gradle Ignore source / target compatibility?

Question

My Java 7 project builds fine in Gradle, although it depends on java.util.Optional .

I am very, very confused. java.util.Optional was just the thing in Java 8, right?

I have a Gradle project and I set both sourceCompatibility and targetCompatibility to 1.7 .

In one class in this module, I import java.util.Optional , which I thought was not included before Java 8.

If I run gradlew clean assemble , the compiler even gets calls with the correct parameters. However, there is a warning that sounds a little suspicious. However, the flask was built just fine.

 15:51:12.998 [DEBUG] [org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter] Executing actions for task ':core:compileJava'. 15:51:13.000 [DEBUG] [org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler] Compiler arguments: -source 1.7 -target 1.7 -d /Users/deejay/workspace/number-jumble/core/build/classes/main -g -encoding UTF-8 -classpath /Users/deejay/workspace/number-jumble/model/build/libs/model-1.0.jar:/Users/deejay/.gradle/caches/modules-2/files-2.1/com.badlogicgames.gdx/gdx/1.3.1/18995f8b7b19118975722370818023c76a86fdf4/gdx-1.3.1.jar:/Users/deejay/.gradle/caches/modules-2/files-2.1/com.badlogicgames.gdx/gdx-freetype/1.3.1/1f647429753c8c91fb8fc477ffe5a4c9cde2f429/gdx-freetype-1.3.1.jar:/Users/deejay/.gradle/caches/modules-2/files-2.1/com.google.guava/guava/18.0/cce0823396aa693798f8882e64213b1772032b09/guava-18.0.jar /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/NumberJumbleGame.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/complexity/ChangeComplexityScreen.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/libgdx/SizeToAndLayoutAction.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/libgdx/TimeLabel.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/services/AppropriatelySizedFontService.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/services/DateService.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/session/GameSessionUi.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/session/HardcodedStreakAssessmentService.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/session/LandscapeGameSessionUi.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/session/PortraitGameSessionUi.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/session/RackScreen.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/session/RackSummaryScreen.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/session/StreakAssessmentService.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/splash/ReturnSplashScreen.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/stats/GdxLocalStatisticsRepository.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/stats/MapBackedStatisticsRepository.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/stats/StatisticsRepository.java /Users/deejay/workspace/number-jumble/core/src/main/java/com/binarytweed/numberjumble/stats/StatisticsService.java 15:51:13.001 [INFO] [org.gradle.api.internal.tasks.compile.jdk6.Jdk6JavaCompiler] Compiling with JDK Java compiler API. 15:51:13.007 [ERROR] [system.err] warning: [options] bootstrap class path not set in conjunction with -source 1.7 15:51:13.185 [ERROR] [system.err] 1 warning 

I've gone crazy?

Answer 1

You will not go crazy: D

java.util.Optional was introduced in Java 8. This is correct. And I think you are compiling against Java 8. Thus, the classes used (and tested) are actually Java 8.

sourceCompatibility affects only the syntax styles used. Unused classes. If this parameter is 1.7, you cannot use lambda expressions, for example. But you can use Java 8 classes. However, if you use the new java classes, your application will fail at runtime.

targetCompatibility only affects the compiled language level. Thus, the binary version of Java. Again, access to java classes is possible at compile time, but it will fail if it runs with an older version of java, simply because the reference class is missing.