// Double-check idiom for lazy initialization of instance fields
private volatile FieldType field;

private FieldType getField() {
    FieldType result = field;

    if (result == null) {  // First check (no locking)
        synchronized(this) {
            if (field == null)  // Second check (with locking)
                field = result = computeFieldValue();
        }
    }
    return result;
}

// VS

private FieldType getFieldFixed() {
    FieldType result = field;

    if (result == null) {  // First check (no locking)
        synchronized(this) {
            // Missing assignment above
            // Needs to reassing the field in case several threads
            // hit synchronized together and the first one initialized
            // the fields
            // If the 2nd check is done on the field,
            // all further threads return null as result never gets reassigned.
            result = field;
            if (result == null)  // Second check (with locking), in the original code checking the field
                field = result = computeFieldValue();
        }
    }
    return result;
}