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package singleton.classloading;
/**
* This example shows that you need to be careful to ensure that
* singletons are not accessed before they are created!
*/
class S {
private static S instance;
public static int numInstances;
public static S getInstance() {
if (instance == null) {
instance = new S();
}
return instance;
}
private S() {
S.numInstances++;
B.doNothing(); // B is loaded here, during A's constructor
}
}
class B {
// B caches the only instance of S
public static S a = S.getInstance();
public static void doNothing() {}
}
class Main {
public static void main(String[] args) {
System.out.println(S.getInstance() == B.a); // false!
System.out.println(S.numInstances); // 2!
}
}
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