Question

I want less methods. I want a common global TestClass from which I could use any of its value inside the class.

import java.util.*;
import java.io.*;

public class TestClass {
        TestClass(String hello){
                String hallo = hello;
                String halloSecond = "Saluto!";
        }
        public static void main(String[] args) {
                TestClass test = new TestClass("Tjena!");
                System.out.println("I want "Tjena!": " + test.hallo);
                TestClass testSecond = new TestClass("1");
                System.out.println("I want Saluto!:" + test.halloSecond);
                System.out.println("I want Saluto!:" + testSecond.halloSecond);

                // How can I get glob.vars like the "Saluto!"?
        }
}

[Clarification Needed] I cannot understand the no-use of GLOB.VARS. Please, see the code belowe where you cannot access the GLOB.VARS without an instance, hence the error. If I quarantee no malicious code can make an instance, is there any problem in using GLOB.vars?

$ javac TestClass.java 
TestClass.java:19: non-static variable hallo cannot be referenced from a static context
  System.out.println("It did not get to the GLOB.VAR: " + hallo);
                                             ^
1 error
$ cat TestClass.java 
import java.util.*;
import java.io.*;

public class TestClass {
        public String hallo;
        public String halloSecond;

        TestClass(String hello){
                hallo = hello;
                halloSecond = "Saluto!";
        }
        public static void main(String[] args) {
                TestClass test = new TestClass("Tjena!");
      System.out.println("It did not get to the GLOB.VAR" + hallo);
        }
}

Answer 1

I guess you are looking for something like this:

public class TestClass {
    public final String hallo;
    public static final String halloSecond = "Saluto!";

    TestClass(String hello){
        String hallo = hello;
    }

    public static void main(String[] args) {
        TestClass test = new TestClass("Tjena!");
        System.out.println("I want "Tjena!": " + test.hallo);
        TestClass testSecond = new TestClass("1");
        System.out.println("I want Saluto!:" + test.halloSecond);
        System.out.println("I want Saluto!:" + testSecond.halloSecond);
    }
}

The value of hallo is set in each instance of TestClass. The value of halloSecond is a constant, shared by all instances of the class and visible for the whole app. Note that with this code your IDE/compiler probably gives you a warning upon test.halloSecond – it should be qualified by the class name, like TestClass.halloSecond, rather than an instance name.

Update on global variables: the main problem with global variables is that they make the code

• harder to understand – if a method uses global variables, you can’t see simply from its signature what data is it actually manipulating
• harder to test – same method is difficult to test isolated in unit tests, as you have to (re)set all global variables it depends on to the desired state before each unit test
• harder to maintain – global variables create dependencies, which easily make the code into a tangled mess where everything depends on everything else

In Java everything is inside a class, so you can’t have “classic” global variables like in C/C++. However, a public static data member is still in fact a global variable.

Note that the code sample above, halloSecond is a global constant, not a variable (as it is declared final and is immutable), which alleviates much of these problems (except maybe the dependency issue).