Import on demand class.asterisk

[Sergej Smoljanov]

import java.lang.String.*;

there is no compilation error. (i use javac/java and NetBeans - same result all ok)
I expect String is not package, why import on demand allowed?

what rule for this, and what purpose of this behaviour?

[K. Tsang]

Apart from the import, how are you using the methods of the String class?

[Sergej Smoljanov]

i thisk for import member (static method) of class use:

import static java.lang.String.*

(String is only example, same with Byte and others)
and for non static import i think it used for import type, like

import java.util.ArrayList

and if in path there is no right package - had compilation error.
Is this behaviour made for inner classes/interface? (that may be or not in class)

[Paweł Baczyński]

Well, importing java.lang.String.* is allowed because String (well, any class) can have public static nested classes declared inside.

[Roel De Nijs]

Any class (even interfaces) can have (static) nested classes. That's why that import-statement is allowed. This is illustrated in a small code example.

Assume this class:

package com.ocajp7;
public class MyClass {
public static class MyStaticInnerClass1{}
public class MyInnerClass2 {}
}

And this test class:

import com.ocajp7.MyClass; // import1
import com.ocajp7.MyClass.*; // import2
public class TestMyClass {
public static void main(String[] args) {
MyClass clazz = new MyClass(); // line1
MyStaticInnerClass1 clazz1a = new MyStaticInnerClass1(); // line2
MyInnerClass2 clazz2 = clazz.new MyInnerClass2(); // line3
MyClass.MyStaticInnerClass1 clazz1b = new MyClass.MyStaticInnerClass1(); // line4
}
}

Some observations about this code:

Without import1, line1 and line4 won't compile.

Without import2, line2 and line3 won't compile (but line4 will compile).

Disclaimer: inner classes are not on the OCAJP7 exam.