Eclipse和Maven之间类型转换的不同编译行为

Question

Here is my code example:

private static void fac(Map<? extends Serializable,? extends Serializable> mapTo){
    //do sth.
}

public static void main(String[] args) {
    Map<String,Object> mapFrom=null;
    fac((Map<? extends Serializable, ? extends Serializable>) mapFrom);     
}

The code above is compiled successfully in eclipse(with a type safety warning) but failed in maven(an "incompatible types" error caused by javac?).

Now I have to change my code like this:

public static void main(String[] args) {
    Map<String,Object> mapFrom=null;
    fac((Map) mapFrom);     
}

I've confirmed the java version is the same, and my question is:

1. Why do they have different behavior?

2. What's the preferred way to write the code?

Answer 1

Eclipse comes with its own Java compiler; Maven uses javac . Most of the time, both accept the same code but generics are complicated and compiler do have bugs. There are a couple of known bugs in javac of Java 6 which cause problems, for example.

Oracle will not fix them. The solution is to use Java 7 to run Maven and configure the maven-compiler-plugin the generate Java 6 byte code (see Kumar Sambhav's answer ).

Answer 2

Try adding this plugin (inside build->plugins-> tag) to your pom.xml :-

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.0</version>
            <configuration>
                <source>1.6</source>
                <target>1.6</target>
            </configuration>
        </plugin>

This will ensure the compiler version to be used with your project.