Java：如何排除java.lang类的隐式导入

Question

例如，如果我想排除加载java.lang.String，我将如何去做？

Answer 1

Write your own compiler, that can compile this new, almost-Java language.

In Java,

Code in a compilation unit automatically has access to all types declared in its package and also automatically imports all of the public types declared in the predefined package java.lang .

There is no way to disable that behavior. And you don't need to; imports only affect compilation, and even if a type was (unwisely) named the same as a java.lang type, like Object , you can reference it with its fully qualified name in source code.

Answer 2

You're mixing up two topics.

The heading reads "How to Exclude Implicit Import of java.lang classes", and in the body you ask about "exclude loading java.lang.String".

The automatic import of java.lang.* has no influence whatsoever on the runtime. It only allows you at compile-time to reference strings with the simple word String instead of the dot-construct java.lang.String .

The class java.lang.String will be loaded if and only if your code needs it , no matter if you referenced it as String or as java.lang.String in your source code.

And I am VERY SURE that every Java program needs the String class, eg in its public static void main(String[] args) plus in lots of library classes.

So, if you worry about memory footprint so much that loading the String class might become a problem, switch to a different language, eg K&R C from the 1970s.