CODEWITHSUNDEEP
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Suhail Gupta
Suhail Gupta

Reputation: 23256

Why do I get the default false when I set the boolean : true?

Let there be three classes named Tester_1 ,Tester_2,Tester_3. They are defined as :

Tester_1:

class Tester_1 {

 public static void main(String args[]) {
    Tester_2.setBoolean(true);
    System.out.println(Tester_2.getBoolean());
 }
}

Tester_2:

class Tester_2 {

public static boolean var = false; // Static var

public static void setBoolean(boolean value) {
   var = value;
}

public static boolean getBoolean() {
    return var;
}

}

Tester_3:

class Tester_3 {
public static void main(String args[]) {
    System.out.println(Tester_2.getBoolean());
}
}

After I compile all the three classes, I run them in the following order :

java Tester_1

java Tester_3

but I get this output :

true from the first run and false from the second run. Why is that ? When Tester_1 sets the boolean to a value true why do I get the default false when I run Tester_3 ?

Upvotes: 3

Views: 129

Answers (4)

Azodious
Azodious

Reputation: 13872

java Tester_1

This is 1st run of program. (i.e. a process)

java Tester_3

This is 2nd run of program. (another process)

static values persist within a process. not across processes.

Upvotes: 0

Vinay Veluri
Vinay Veluri

Reputation: 6855

Two separate executions --> different results.

JVM turns it more interesting as it erases previous data for every execution.

Upvotes: 0

mprivat
mprivat

Reputation: 21902

Because static variables hold their value staticly within the JVM, but is not held across JVMs. Once the JVM process exits, it's variable values in memory are destroyed. When the second JVM is started, then everything is reinitialized.

If you need to keep values across runs, you will have to persist them somewhere (to the file system or a database for example).

Upvotes: 1

assylias
assylias

Reputation: 328629

static is only valid at the Java Virtual Machine (JVM) level.

Each time you call java xxx you create a new JVM which does not share anything with the previous call => all static variables get their default value again.

Upvotes: 7

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