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Java Maven build source and targe is not working

I have JDK 7 and 8 installed in my PC.

I try to set JAVA_HOME to JDK 8 and in the maven pom file, I set to 1.7 as below:

<properties>
    <maven.compiler.target>1.7</maven.compiler.target>
    <maven.compiler.source>1.7</maven.compiler.source>
</properties>

I got the error below during maven build:

incomparable types: boolean and java.lang.Object

The source code is:

Map mapData = (LinkedHashMap)it.next();
if(true == mapData.get("isTrueOrFalse")){ // java 8 doesn't allow this, it have to be [true == (boolean)mapData.get("isTrueOrFalse")]
    xxx
}

I can't change the source code, so I change my JAVA_HOME to JDK 7 and maven pom remain as 1.7. Then I can successfully build via Maven.

My understanding is, by setting the source and target, it should allow me to compile onto lower compatible Java version, but it is not. Can anyone help to explain this?

Solution

  • After so many of searching of Java compatibility post, I found two possible reasons why this is happening:

    1) this is a bug in JDK 7, it should not allow JDK 7 to compile this as the type is not match. This is fixed in JDK 8, so even we use the -source=1.7 and -target=1.7, it is not allowed to go through. JDK 1.7 breaks backward compatibility? (generics)

    2) this might due to the Java implementation return type not compatible, while using JDK 8 compile to -source=1.7 and -target=1.7, the build path (bootstrap classes) will be still pointing to JDK 8, as so the implementation of Java Map may return different type which cause issue above. Issue about java 8 backward compatibility: new methods in JDK