Compiling GWT 2.6.1 at Java 7 source level

Question

I've recently updated my GWT project to 2.6.1, and started to make use of Java 7 syntax since 2.6 now supports Java 7.

However, when I attempt to compile, I'm receiving compiler errors such as

[ERROR] Line 42: '<>' operator is not allowed for source level below 1.7

Full output

Compiling module com.Project
   Validating units:
      Ignored 85 units with compilation errors in first pass.
Compile with -strict or with -logLevel set to TRACE or DEBUG to see all errors.
   Computing all possible rebind results for 'com.google.gwt.useragent.client.UserAgentAsserter'
      Rebinding com.google.gwt.useragent.client.UserAgentAsserter
         Checking rule <generate-with class='com.google.gwt.editor.rebind.SimpleBeanEditorDriverGenerator'/>
            [WARN] Detected warnings related to 'com.google.gwt.editor.client.SimpleBeanEditorDriver'.   Are validation-api-<version>.jar and validation-api-<version>-sources.jar on the classpath?
            Specify -logLevel DEBUG to see all errors.
            [WARN] Unknown type 'com.google.gwt.editor.client.SimpleBeanEditorDriver' specified in deferred binding rule
   [ERROR] Errors in 'file:/C:/workspace/Project/src/com/project/ProjectFile.java'
      [ERROR] Line 42: '<>' operator is not allowed for source level below 1.7
   [ERROR] Errors in 'file:/C:/workspace/Project/src/com/project/AnotherProjectFile.java'
      [ERROR] Line 188: Cannot switch on a value of type String for source level below 1.7. Only convertible int values or enum variables are permitted
C:\workspace\Project\build.xml:51: Java returned: 1
    at org.apache.tools.ant.taskdefs.Java.execute(Java.java:111)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:291)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.Target.execute(Target.java:390)
    at org.apache.tools.ant.Target.performTasks(Target.java:411)
    at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1399)
    at org.apache.tools.ant.Project.executeTarget(Project.java:1368)
    at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
    at org.apache.tools.ant.Project.executeTargets(Project.java:1251)
    at org.apache.tools.ant.Main.runBuild(Main.java:809)
    at org.apache.tools.ant.Main.startAnt(Main.java:217)
    at org.apache.tools.ant.Main.start(Main.java:180)
    at org.apache.tools.ant.Main.main(Main.java:268)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.ant.execution.AntMain2.main(AntMain2.java:30)
C:\workspace\Project\build.xml:51: Java returned: 1
    at org.apache.tools.ant.taskdefs.Java.execute(Java.java:111)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:291)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.Target.execute(Target.java:390)
    at org.apache.tools.ant.Target.performTasks(Target.java:411)
    at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1399)
    at org.apache.tools.ant.Project.executeTarget(Project.java:1368)
    at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
    at org.apache.tools.ant.Project.executeTargets(Project.java:1251)
    at org.apache.tools.ant.Main.runBuild(Main.java:809)
    at org.apache.tools.ant.Main.startAnt(Main.java:217)
    at org.apache.tools.ant.Main.start(Main.java:180)
    at org.apache.tools.ant.Main.main(Main.java:268)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.ant.execution.AntMain2.main(AntMain2.java:30)
C:\workspace\Project\build.xml:51: Java returned: 1
    at org.apache.tools.ant.taskdefs.Java.execute(Java.java:111)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:291)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.Target.execute(Target.java:390)
    at org.apache.tools.ant.Target.performTasks(Target.java:411)
    at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1399)
    at org.apache.tools.ant.Project.executeTarget(Project.java:1368)
    at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
    at org.apache.tools.ant.Project.executeTargets(Project.java:1251)
    at org.apache.tools.ant.Main.runBuild(Main.java:809)
    at org.apache.tools.ant.Main.startAnt(Main.java:217)
    at org.apache.tools.ant.Main.start(Main.java:180)
    at org.apache.tools.ant.Main.main(Main.java:268)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.ant.execution.AntMain2.main(AntMain2.java:30)

How do I specify the GWT compiler to target 1.7? I was under the impression that it would do that by default, but I guess not. I've attempted cleaning the project, including deleting the gwt-unitCache directory but to no avail.

Here is my Ant compile target.

<target name="compile" depends="prepare">
    <javac includeantruntime="false"
           debug="on"
           debuglevel="lines,vars,source"
           srcdir="${src.dir}"
           destdir="${build.dir}"
           source="7"
           target="7">
        <classpath refid="project.classpath"/>
    </javac>
</target>

<target name="gwt-compile" depends="compile">
    <java failonerror="true" fork="true" classname="com.google.gwt.dev.Compiler">
        <classpath>
            <!-- src dir is added to ensure the module.xml file(s) are on the classpath -->
            <pathelement location="${src.dir}"/>
            <pathelement location="${build.dir}"/>
            <path refid="project.classpath"/>
        </classpath>
        <jvmarg value="-Xmx256M"/>
        <arg value="-sourceLevel"/><arg value="7"/>
        <arg value="${gwt.module.name}"/>
    </java>
</target>

Answer 1

The GWT Compiler (and SuperDevMode's CodeServer) has a -sourceLevel argument that you can use to specify the language level, similar to the -source argument of javac.

The default value of -sourceLevel depends on your current JVM, so it should default to Java 7 if you use a JDK 1.7.

It's a good practice to be explicit and pass -sourceLevel 7 (or 1.7) to GWT, anda -source 7 (or 1.7) to javac (use source="7" in your <javac> Ant task)