Java Core Classes and Threads

The getInitParameter(String name) method of a Servlet returns a String containing the value of the named initialization parameter, or null if the parameter does not exist. Other methods like getServletContext() do not return null.

To sort the keys in the props HashMap, the user needs to know about the different data structures available in Java that can help to sort a collection of keys. The user also needs to know about the methods provided by the Java Collections framework that can be used to perform sorting on collections.

Option A: Arrays.sort(s); is incorrect. The Arrays.sort() method is used to sort arrays, not sets or maps. It will result in a compilation error.

Option B: s = new TreeSet(s); is correct. A TreeSet is a sorted set that orders its elements based on their natural ordering or based on a comparator provided at the time of creation. By creating a new TreeSet using the Set of keys from the props HashMap, the keys will be automatically sorted.

Option C: Collections.sort(s); is incorrect. The Collections.sort() method is used to sort lists, not sets or maps. It will result in a compilation error.

Option D: s = new SortedSet(s); is incorrect. SortedSet is an interface and cannot be instantiated. Moreover, the Set obtained from the props HashMap is already sorted.

Therefore, the correct answer is:

The Answer is: B. s = new TreeSet(s);

JavaBeans getter methods follow the pattern get where the property name starts lowercase. getCust() correctly accesses a property named cust. The other options don't follow JavaBeans conventions: addSize sounds like a bulk operation, deleteRep and putDimensions don't use the get prefix for accessors.

A NullPointerException in Flow tracing most commonly occurs when trying to access a pipeline variable that doesn't exist because a required input wasn't set or mapped. Options B, C, and D cause different errors (branch on NULL, exit signal failure, or no loop array), not necessarily NPE.

In Java, a top-level class cannot be private - only public, abstract, and final are allowed. The code attempts to declare "private class AQuestion" which violates this rule. Therefore, the code does not compile. If it were a valid inner class, the overload resolution would select the more specific String method for null argument.

The action flushes the response buffer before including the target resource. Once headers are sent (which happens during the flush), you cannot set cookies because cookies require HTTP headers. Any attempt to add cookies via response.addCookie() after a jsp:include will fail or be ignored.

Calling request.getSession(false) retrieves the current active session associated with the request. If no session exists, it returns null instead of creating a new one, which is useful for checking session validity without overhead.

In Java, once a thread completes its execution and enters the dead (terminated) state, it cannot be restarted. Attempting to call the start() method again on a dead thread will throw an IllegalThreadStateException.

The com.bluemartini.dna.Callback interface requires implementation of the execute() method, which takes a DNAList input parameter and returns a DNAList. This is the standard callback pattern for custom business logic execution in Blue Martini's DNA framework.

Java's Thread and Object classes support wait(), run(), and sleep() (note: lowercase sleep is standard, but begin is completely non-existent in Java thread APIs), making begin() the correct answer.

It is false to claim that a HashMap cannot be made synchronized. You can easily obtain a synchronized wrapper using Collections.synchronizedMap(new HashMap()) or use ConcurrentHashMap.

ListIterator is an interface that extends Iterator, not an implementation (class). Implementations include classes like ArrayList.ListIter. The statement is false.

Collection is in java.util package. java.lang is for core classes like String, Object. java.util.Collections (plural) is a utility class, not the Collection interface.