java – JDK8 with -source 1.7 [默认方法]

我有以下课

public class zoneddatetimeToInstant {

    public static void main(final String[] args)
        throws NoSuchMethodException {

        assert Chronozoneddatetime.class.isAssignableFrom(zoneddatetime.class);
        final Method toInstant
            = Chronozoneddatetime.class.getmethod("toInstant");

        final zoneddatetime Now = zoneddatetime.Now();
        final Instant instant = Now.toInstant();

        System.out.println(instant);
    }
}

它只是编译罚款.

& javac zoneddatetimeToInstant.java

并且它与-source 1.7失败.

& javac -source 1.7 zoneddatetimeToInstant.java
zoneddatetimeToInstant.java:10: error: cannot find symbol
    final Instant instant = Now.toInstant();
                               ^
  symbol:   method toInstant()
  location: variable Now of type zoneddatetime
1 error
1 warning

这是正常吗？看来javac不了解除1.8以外的-source的JDK类.

根据javac,javac仍然支持各种-source版本选项,就像以前的版本一样.

补充

我已经知道JSR 310: Date and Time API仅在Java 8中可用.与javac有什么关系？

$cat Java8.java
public class Java8 {
    public void print(java.io.PrintStream out) {
        out.printf("hello world\n");
    }
}
$javac Java8.java
$cat Java7.java
public class Java7 {
    public static void main(final String[] args) {
        new Java8().print(System.out);
    }
}
$javac -source 1.7 -target 1.7 Java7.java
warning: [options] bootstrap class path not set in conjunction with -source 1.7
1 warning
$java Java7
hello world

结论

正如@ Eng.Fouad所说.问题是该方法是在接口中定义的默认方法. javac似乎抓住了这一点.

$cat Java8i.java
public interface Java8i {
    default void print(java.io.PrintStream out) {
        out.printf("hello world\n");
    }
}
$javac Java8i.java
$cat Java8c.java
public class Java8c implements Java8i {
}
$javac Java8c.java
$cat Java7i.java
public class Java7i {
    public static void main(final String[] args) {
        new Java8c().print(System.out);
    }
}
$javac -source 1.7 -target 1.7 Java7i.java
warning: [options] bootstrap class path not set in conjunction with -source 1.7
Java7i.java:3: error: cannot find symbol
    new Java8c().print(System.out);
                ^
  symbol:   method print(PrintStream)
  location: class Java8c
1 error
1 warning

javac应该更有帮助地告诉我.

解决方法

这是在Java 8中引入的新的Time / Date API.这就是为什么它不能用Java 7编译.

toInstant()是一个默认方法,而-source 1.7不支持默认方法(Java 8的新功能).