玩玩java classpath package import

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On:
In: java

这几天碰到了编译失败的严重问题，所以只好痛下心来好好研究看看：

我的OS:Windows XP

有设PATH：C:Program FilesJavajdk1.6.0_07bin

package要用的程式码Fish.java：

package water;

public class Fish {
public static String name = “小金”;
public static String type = “金鱼”;
public static String color = “金”;
public static void skill() {
System.out.println(“吐泡泡”);
}
}

import 要用的程式码PetStore3.java：

import water.*;

public class PetStore3 {
public static void main(String[] args) {
String fishName = Fish.name;
String fishKind = Fish.type;
String fishColor = Fish.color;
System.out.println(“我有一只优雅的” + fishKind +
“, 名叫” + fishName +
“, 他的颜色是”+fishColor+” 色的.”);
System.out.println(“每当他肚子饿的时候都会”);
Fish.skill();
}
}

分14种状况测试，这真的很好玩，结果有令人恍然大悟的感觉：

Fish.java位置 classpath设定 PetStore3.java位置 结果
c:\water .; c:\ OK
c:\water .; c:\water PetStore3.java:1: package water does not exist
import water.*;
^
PetStore3.java:5: cannot access Fish
bad class file: .Fish.class
class file contains wrong class: water.Fish
Please remove or make sure it appears in the correct subdirectory of the classpa
th.
String fishName = Fish.name;
^
2 errors
c:\water .;c:\; c:\water PetStore3.java:5: cannot access Fish
bad class file: d:sourcejavawaterFish.class
class file contains wrong class: water.Fish
Please remove or make sure it appears in the correct subdirectory of the classpa
th.
String fishName = Fish.name;
^
1 error
c:\water .;c:\; c\: OK
c:\source\water .; c:\ PetStore3.java:1: package water does not exist
import water.*;
^
PetStore3.java:5: cannot find symbol
symbol  : variable Fish
location: class PetStore3
String fishName = Fish.name;
^
PetStore3.java:6: cannot find symbol
symbol  : variable Fish
location: class PetStore3
String fishKind = Fish.type;
^
PetStore3.java:7: cannot find symbol
symbol  : variable Fish
location: class PetStore3
String fishColor = Fish.color;
^
PetStore3.java:12: cannot find symbol
symbol  : variable Fish
location: class PetStore3
Fish.skill();
^
5 errors
c:\source\water .;c:\; c:\ PetStore3.java:1: package water does not exist
import water.*;
^
PetStore3.java:5: cannot find symbol
symbol  : variable Fish
location: class PetStore3
String fishName = Fish.name;
^
PetStore3.java:6: cannot find symbol
symbol  : variable Fish
location: class PetStore3
String fishKind = Fish.type;
^
PetStore3.java:7: cannot find symbol
symbol  : variable Fish
location: class PetStore3
String fishColor = Fish.color;
^
PetStore3.java:12: cannot find symbol
symbol  : variable Fish
location: class PetStore3
Fish.skill();
^
5 errors
c:\source\water .;c:\source; c:\ OK
c:\source\water .; c:\source OK
c:\source\water .;c:\; c:\source OK
c:\source\water .;c:\source; c:\source OK
c:\source\water .;any path; c:\source OK（主要是classpath设.的关系）
c:\source\java\water .; c:\ package water does not exit;
c:\source\java\water .; c:\source package water does not exit;
c:\source\java\water .; c:\source\java OK
d:\source\java\water .; d:\source\java package water does not exit;

噫！”.”不是依照目前的目录去找package的class吗？可是放在d:时，好像就不是这样了，看来java的编译规则的classpath的”.”是指针对c:讲的，我终于有点恍然大悟，但是很多课本及网页都说是依照目前的目录去搜寻class的path，看来是有很大的争议的，不过有这个测试之后，感觉厘清了很多观念！