錯誤：從包編譯Java文件P2

Question

package p1; 
public class Protection { 

int n = 1; 
private int n_pri = 2; 
protected int n_pro = 3; 
public int n_pub = 4; 

public Protection() { 
    System.out.println("base constructor"); 
    System.out.println("n = " + n); 
    System.out.println("n_pri = " + n_pri); 
    System.out.println("n_pro = " + n_pro); 
    System.out.println("n_pub = " + n_pub); 
} 
} 

包P2包P1不存在包含三個文件demo.java，OtherPackage.java和Protection2.java：

//Demo package p2. 
package p2; 

//Instantiate various classes in p2. 
public class Demo { 
public static void main(String[] args) { 
    Protection2 ob1 = new Protection2(); 
    OtherPackage ob2 = new OtherPackage(); 
} 
} 

package p2; 

OtherPackage.java

class OtherPackage { 
OtherPackage() { 
    p1.Protection p = new p1.Protection(); 
    System.out.println("Other package constructor"); 

    //class or package only 
    //System.out.println("n = " + p.n); 

    //class only 
    //System.out.println("n_pri = " + p.n_pri); 

    //class, subclass or package only 
    //System.out.println("n_pro = " + p.n_pro) 

    System.out.println("n_pub = " + p.n_pub); 
} 
} 

和Protection2.java

package p2; 

class Protection2 extends p1.Protection { 
Protection2() { 
    System.out.println("Derived other package constructor"); 

    //class or package only 
    //System.out.println("n = " + n); 

    //class only 
    //System.out.println("n_pri = " + n_pri); 

    System.out.println("n_pro = " + n_pro); 
    System.out.println("n_pub = " + n_pub); 
} 
} 

我試圖從包P2編譯Demo.java：

:~/Desktop/Examples/p2$ javac *.java 

I產生以下錯誤

Protection2.java:3: error: package p1 does not exist 
class Protection2 extends p1.Protection { 
         ^
OtherPackage.java:5: error: package p1 does not exist 
    p1.Protection p = new p1.Protection(); 
    ^
OtherPackage.java:5: error: package p1 does not exist 
    p1.Protection p = new p1.Protection(); 
          ^
Protection2.java:13: error: cannot find symbol 
    System.out.println("n_pro = " + n_pro); 
            ^
    symbol: variable n_pro 
    location: class Protection2 
Protection2.java:14: error: cannot find symbol 
    System.out.println("n_pub = " + n_pub); 
            ^
    symbol: variable n_pub 
    location: class Protection2 
5 errors 

我試圖導入包P1，但它與上述5個錯誤沿着增加了另一個錯誤：

Demo.java:4: error: package p1 does not exist 
import p1.Protection; 

Answer 1

我做了這個目錄結構：

    package 
        | 
     ---------------------------- 
     |       | 
    source      bin 
     |       | 
(All .java files)  (Package folders after compilation) 

個

Java文件：

Protection.java

package p1; 

public class Protection { 

    public int m_Pub; 

    int m_N; 
    private int m_Pri; 
    protected int m_Pro; 

    public Protection() { 
     m_Pub = 4; 
     m_N = 1; 
     m_Pri = 2; 
     m_Pro = 3; 

     System.out.println ("Base Constructor"); 
     System.out.println ("m_Pub = " + m_Pub); 
     System.out.println ("m_N = " + m_N); 
     System.out.println ("m_Pri = " + m_Pri); 
     System.out.println ("m_Pro = " + m_Pro); 
    } 
} 

Demo.java

package p2; 

public class Demo { 

    public static void main (String [] args) { 
     Protection2 protection2 = new Protection2(); 
     OtherPackage otherPackage = new OtherPackage(); 
    } 
} 

OtherPackage.java

package p2; 

import p1.Protection; 

public class OtherPackage { 

    public OtherPackage() { 
     Protection protection = new Protection(); 
     System.out.println ("OtherPackage Constructor"); 
    } 
} 

Protection2.java

package p2; 

import p1.Protection; 

public class Protection2 extends Protection { 

    public Protection2() { 
     System.out.println ("Derived Protection2 Constructor"); 
     System.out.println ("m_Pro = " + m_Pro); 
     System.out.println ("m_Pub = " + m_Pub); 
    } 
} 

彙編：

nipal_000@Lenovo-PC /cygdrive/c/mine/java/package 
$ javac -d bin source/*.java 

執行：

nipal_000@Lenovo-PC /cygdrive/c/mine/java/package 
$ cd bin 

nipal_000@Lenovo-PC /cygdrive/c/mine/java/package/bin 
$ java p2.Demo 
Base Constructor 
m_Pub = 4 
m_N = 1 
m_Pri = 2 
m_Pro = 3 
Derived Protection2 Constructor 
m_Pro = 3 
m_Pub = 4 
Base Constructor 
m_Pub = 4 
m_N = 1 
m_Pri = 2 
m_Pro = 3 
OtherPackage Constructor 

nipal_000@Lenovo-PC /cygdrive/c/mine/java/package/bin 

問題在於，編譯時未能指定，在哪裏查找package p1，因爲您位於文件夾p2內。在編譯過程中，您需要放置所有.java文件。

如果你試圖讓每個.java文件在其各自的package文件夾，然後它是這樣的：

目錄結構：

     package 
         | 
      ---------------------------- 
      |       | 
     source      bin 
      |       | 
    ------------  (Package folders after compilation) 
    |   | 
    p1   p2 
    |   | 
    |  Demo.java OtherPackage.java Protection2.java 
Protection.java 

編譯：

nipal_000@Lenovo-PC /cygdrive/c/mine/java/package 
$ javac -d bin source/p1/*.java source/p2/*.java 

執行：

nipal_000@Lenovo-PC /cygdrive/c/mine/java/package 
$ cd bin 

nipal_000@Lenovo-PC /cygdrive/c/mine/java/package/bin 
$ java p2.Demo 
Base Constructor 
m_Pub = 4 
m_N = 1 
m_Pri = 2 
m_Pro = 3 
Derived Protection2 Constructor 
m_Pro = 3 
m_Pub = 4 
Base Constructor 
m_Pub = 4 
m_N = 1 
m_Pri = 2 
m_Pro = 3 
OtherPackage Constructor 

nipal_000@Lenovo-PC /cygdrive/c/mine/java/package/bin