如何在两个Java文件中使用相同的字符串

Question

Sorry for my bad English and for maybe stupid question but I'm new in Java.

I need use same string in 2 java files for example:

In first java file I've got code for sending emails, I've got string set to default email:

public String mail = new String ("lala@gmail.com");

and I use this string in code for send email:

email.addTo(mail);

In second java file something like set up where can user set new email address I want to have same string, connected with string in first java file. When user put new email String mail will be change to new email address and in email.addTo(mail); will be use this new address

How can I do this?

Answer 1

use Shared Preferences, you can store it as key-value Pair. value being your email and key can be any unique string which you want to identify it with.

Answer 2

I'm a bit confused with the question, but I'll take a stab at it. Basically, you would like to have one String in a given file be used in multiple locations. This is easily done using class-level variables and making them publicly accessible.

For example, in the file:

EmailObject.java

public class EmailObject {

    public static final String mail = "lala@gmail.com";

    // The rest of your code
}

Another file can access this like so:

OtherObject.java

public void sendEmail() {
     EmailMessage email = new EmailMessage();
     email.addTo(EmailObject.mail);
}

Note the static and final modifiers on the original. This ensures that you do not need an actual instance of EmailObject to access the string and it also ensures that the string is never modified accidentally by some other object.

There are, of course, other ways to do this, but this one matches your code the most. This is also a very "Java" solution. Android has other ways to share data (as indicated by the other answer).

Answer 3

The simplest way that I would not recommend is to have a public static field:

class A {
   public static String commonString;
}

class B {

   public void methodThatUsesString () {
      // Do stuff with the string
      Log.d("I have the string", A.commonString);
   }
}

If you have two Activities, and one starts another, you can send data through Intents.

The forementioned SharedPreferences way is a good solution too, if the email address is a persistent thing, a preference if you will, and not just data reqired for an operation.

You can keep a reference of one instance of a class in the otherone, and access it's fields through it:

class A {
   public String commonString;
}

class B {
   private final A instaceOfA;

   public B (A instanceOfA) {
      this.instanceOfA = instanceOfA;
   }

   public void methodThatUsesString () {
      // Do stuff with the string
      Log.d("I have the string", instanceOfA.commonString);
   }
}

Or even use a getter or setter if performance is not an issue.

Answer 4

Many answers depending on how the string will be used.

• If it's a constant string, one that will never change, never use final static String

  public final static String AUTHOR_MAIL = "lala@gmail.com";

Then you can use it in a static way wherever you want.

email.addTo(MyClass.AUTHOR_MAIL);

• If this String will be used in different Activities you can not access it directly (you can not tell if the other Activity is still alive). You have to use Persistence Mechanisms such as SharedPreferences or directly send needed data in your Intent.

• If it's in a helper class inside your Activity, you can just use mObject.mail to get it.