一个java源文件可以包含多个类,但是只能有一个是 public 的类 而且这个 public 类必须与文件名一样
例如,Test.java中是可以包含其他类的:
class A{
}
class B{
}
public class Test{
}
注意,同一源文件中的非public类不能用其他修饰符修饰:下面定义类A和类B时会报编译错误的:
private class A{
}
protected class B{
}
public class Test{
}
同一源文件中的非public类,其成员变量和成员方法的访问修饰符使用与普通public类相同,类的访问限定效果等同于同一包下未使用public修饰的类:
在包package1下分别定义Test.java和ClassB.java
ClassB.java:(注意是非public类)
package pacakge1;
class ClassB {
public ClassB(int id){
this.id1 =id;
this.id2 =id;
this.id3 =id;
this.id4 =id;
}
private int id1;
protected int id2;
int id3;
public int id4;
}
Test.java:
package pacakge1;
class ClassA{
public ClassA(int id){
this.id1 =id;
this.id2 =id;
this.id3 =id;
this.id4 =id;
}
private int id1;
protected int id2;
int id3;
public int id4;
}
public class Test {
public static void main(String[] args){
ClassA a = new ClassA(1);
System.out.println(a.id2);
System.out.println(a.id3);
System.out.println(a.id4);
ClassB b = new ClassB(2);
System.out.println(b.id2);
System.out.println(b.id3);
System.out.println(b.id4);
}
}
Test.java里面定义的类ClassA相当于与Test.java同一包名下定义的ClassB类.
假如在另一包名package2下增加Test2.java,是会报编译错误的:
package package2;
import package1.*;
public class Test2 {
public static void main(String[] args){
//这句会报编译错误
ClassA a = new ClassA(1);
System.out.println(a.id2);
System.out.println(a.id3);
System.out.println(a.id4);
//这句也会报编译错误
ClassB b = new ClassB(2);
System.out.println(b.id2);
System.out.println(b.id3);
System.out.println(b.id4);
}