Why such solution?

private double param = Math.random();
private StringBuilder sb = new StringBuilder();

private void method0() { // no shared resource involved
    Double d = method3();
}

protected void method1(String param1) { // no shared resource involved
    Solution solution = new Solution();
    solution.method0();
}

public void method2(int param1) { // no shared resource involved
    param1++;
}

synchronized double method3() {
    double random = Math.random();
    param += 40.7; // shared resource modified
    return random + param;
}

private synchronized void method4() { // shared resource modified (StringBuilder not thread safe)
    sb.append(1).append(1).append(1).append(1);
}

protected void method5(String param2) { // no shared resource, pass by value and StringBuffer is thread safe
    new StringBuffer().append(param2).append(param2).append(param2);
}

public synchronized String method6(int param2) {
    System.out.println("Thinking....");
    method7(5e-2);
    sb = new StringBuilder("Got it!"); // shared resource modified
    return sb.toString();
}

String method7(double param2) { // no shared resource, pass by value
    return "" + param2;
}