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| Code Block | ||
|---|---|---|
| ||
public class Lazy {
private static int number;
private static Connection conn;
static {
Thread t = new Thread(new Runnable() {
public void run() {
// Initialize, for example, a database connection
try {
conn = DriverManager.getConnection("connectionstring");
} catch (SQLException e) {
conn = null;
}
Lazy.this.number = 42;
}
});
t.start();
try {
t.join();
} catch(InterruptedException ie) {
throw new AssertionError(ie);
}
// Other initialization
}
public static Connection getConnection() {
if(conn == null) {
throw new IllegalStateException("Connection not initialized");
}
return conn;
}
public static void main(String[] args) {
System.out.println(number);
}
}
|
The code in the static block is responsible for initialization, and starts a background thread. The background thread attempts to assign initialize a database connection and also assigns to the field number but needs to wait until initialization of the Lazy class has finished.
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This compliant solution also uses a static initializer but for initialization and does not spawn a background thread from it.
| Code Block | ||
|---|---|---|
| ||
public class Lazy {
private static int number;
private static Connection conn;
static {
// Initialize, for example, a database connection
this.numbertry {
conn = 42DriverManager.getConnection("connectionstring");
} catch (SQLException e) {
conn = null;
} public static void main(String[] args) {
System.out.println(number)number = 42;
}
// ...
}
|
Compliant Solution (ThreadLocal)
...