?? settrace.java
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import java.lang.reflect.Field;import static java.lang.System.out;enum TraceLevel { OFF, LOW, MEDIUM, HIGH, DEBUG }class MyServer { private TraceLevel level = TraceLevel.OFF;}public class SetTrace { public static void main(String... args) { TraceLevel newLevel = TraceLevel.valueOf(args[0]); try { MyServer svr = new MyServer(); Class<?> c = svr.getClass(); Field f = c.getDeclaredField("level"); f.setAccessible(true); TraceLevel oldLevel = (TraceLevel)f.get(svr); out.format("Original trace level: %s%n", oldLevel); if (oldLevel != newLevel) { f.set(svr, newLevel); out.format(" New trace level: %s%n", f.get(svr)); } // production code should handle these exceptions more gracefully } catch (IllegalArgumentException x) { x.printStackTrace(); } catch (IllegalAccessException x) { x.printStackTrace(); } catch (NoSuchFieldException x) { x.printStackTrace(); } }}
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