Question

我想从包2中访问包1中的变量。

来自包1的类文件TestDriver.java

public class TestDriver {
private static TestDriver instance = new TestDriver();
private static int check;
private static int envt_num;
public static String envt,port,cpy_key;

public Connection con;
private ManageDBConnection mdbc;

private static String ENCRYPTION_KEY = "0123456789abcdef";

public void TestDriver(){
    check = 20;
    Properties prop = new Properties();
    String propFileName = "properties/environment.properties";
    try{
    InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(propFileName);
    System.out.println(inputStream);
    if (inputStream != null) {
        prop.load(inputStream);
        envt = prop.getProperty("envt");
        port = prop.getProperty("port");
        cpy_key = prop.getProperty("cpy_key");
        System.out.println("http://"+envt+"/netprofile/");  
        //Original Login Link
    /*  Constants.driver.get("http://"+prop.getProperty("user").replaceAll("\\s","")+":"+NP_Decrypt.getPassword().replaceAll("\\s","")+"@"+envt+"/netprofile/");
        inputStream.close();*/
        //Added for Local Testing
       String user = prop.getProperty("user");
       String password = prop.getProperty("password");
       Constants.driver.get("http://" + user + ":" + password + "@" + envt + "/test/");


    //  mdbc = new ManageDBConnection();
        //con = mdbc.CreateConnection();
    } else {
        throw new FileNotFoundException("property file '" + propFileName + "' not found in the classpath");
    }
    }catch(Exception e){
        e.printStackTrace();
    }   
}

}

来自包2的类文件Constants.java

 public class Constants 
{
 static Properties prop = new Properties();
// propFileName = "properties/environment.properties";
//TestDriver testdriver = new TestDriver();
 static String envt = TestDriver.envt;
 static String cpy_key = TestDriver.cpy_key;


 //public static final 

 public static final WebDriver driver   = new FirefoxDriver();      

 public static final String InventorySummaryURL     ="http://"+envt+"/test/npHome.do?cpyKey="+cpy_key+"&custId=&grpId=0";    
 public static final String HomeSummary             ="http://"+envt+"/test/npIndex.do?cpyKey="+cpy_key+"&custId=&grpId=0";
 public static final String UploadStatus            ="http://"+envt+"/test/downloadModuleStatus.do?cpyKey="+cpy_key+"&custId=&grpId=0" ;
 public static final String ProfileStatus           ="http://"+envt+"/test/myProfileStatus.do?cpyKey="+cpy_key+"&custId=&grpId=0";

}

在Constants.java中，envt和cpy_key返回的值为零。我想要Package 1中的值。

Answer 1

主要问题是，如果以下变量，您将静态字段与实例字段混淆：

private static final int check;
private static final int envt_num;
private static final String user, password;
public static String envt,port,cpy_key;

整个JVM中的

是相同的，不在实例构造函数中修改它们，相反，您可以创建一个静态块来更新它们的值，并且如果final，您可以将它们标记为public final static String envt,port,cpy_key; static { Properties prop = new Properties(); String propFileName = "properties/environment.properties"; try{ InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(propFileName); System.out.println(inputStream); if (inputStream != null) { prop.load(inputStream); envt = prop.getProperty("envt"); port = prop.getProperty("port"); cpy_key = prop.getProperty("cpy_key"); System.out.println("http://"+envt+"/netprofile/"); //Original Login Link /* Constants.driver.get("http://"+prop.getProperty("user").replaceAll("\\s","")+":"+NP_Decrypt.getPassword().replaceAll("\\s","")+"@"+envt+"/netprofile/"); inputStream.close();*/ //Added for Local Testing user = prop.getProperty("user"); password = prop.getProperty("password"); } else { throw new FileNotFoundException("property file '" + propFileName + "' not found in the classpath"); } } public void TestDriver(){ Constants.driver.get("http://" + user + ":" + password + "@" + envt + "/test/"); // mdbc = new ManageDBConnection(); //con = mdbc.CreateConnection(); }不应该改变。

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关键是将静态字段与实例字段分开，你遇到的问题是静态字段在加载类时没有被初始化，但是在创建实例时。

Jose Luis

Answer 2

变量envt和cpy_key是声明的静态但不应该是。通过将变量声明为静态，您告诉编译器/外部开发人员在使用该变量之前不必实例化此类。

在您的代码中，envt和cpy_key变量仅在TestDriver类的构造函数中初始化。当您从另一个类引用它们而不实例化TestDriver时，您将获得 null 值，该值有时会映射到0。

你能做的是：

从envt和cpy_key变量中删除静态标识符，因为您需要先实例化TestDriver类才能使用它们。
将初始化代码移出构造函数并使用静态初始化块

示例：

public class TestDriver {
private static TestDriver instance = new TestDriver();
private static int check;
private static int envt_num;
public static String envt,port,cpy_key;

public Connection con;
private ManageDBConnection mdbc;

private static String ENCRYPTION_KEY = "0123456789abcdef";

static {
    check = 20;
    Properties prop = new Properties();
    String propFileName = "properties/environment.properties";
    try{
    InputStream inputStream = TestDriver.getClass().getClassLoader().getResourceAsStream(propFileName);
    System.out.println(inputStream);
    if (inputStream != null) {
        prop.load(inputStream);
        envt = prop.getProperty("envt");
        port = prop.getProperty("port");
        cpy_key = prop.getProperty("cpy_key");
        System.out.println("http://"+envt+"/netprofile/");  
        //Original Login Link
    /*      Constants.driver.get("http://"+prop.getProperty("user").replaceAll("\\s","")+":"+NP_Decrypt.getPassword().replaceAll("\\s","")+"@"+envt+"/netprofile/");
        inputStream.close();*/
        //Added for Local Testing
       String user = prop.getProperty("user");
       String password = prop.getProperty("password");
       Constants.driver.get("http://" + user + ":" + password + "@" + envt + "/test/");


    //  mdbc = new ManageDBConnection();
        //con = mdbc.CreateConnection();
    } else {
        throw new FileNotFoundException("property file '" + propFileName + "' not found in the classpath");
    }
    }catch(Exception e){
        e.printStackTrace();
    }   
}

这样可以解决您的初始化问题，但这并不能解决您更大的类设计问题。您应该找到一种更好的（更面向对象的）处理数据的方法。你有两个类依赖于彼此的静态变量。这是一个baaaad计划。我建议你封装需要初始化的变量并将它们保存在TestDriver类中。常量类实际上应该只用于你事先知道的事情（散列键标签，数字常量等）。

从不同的包访问变量

2 个答案: