Java Interview Questions and Answers

Answer - 131 : - Both are synchronized methods. One is instance method, the other is class method. Method with static modifier is a class method. That means the method belongs to class itself and can be accessed directly with class name and is also called Singleton design. The method without static modifier is an instance method. That means the instance method belongs to its object. Every instance of the class gets its own copy of its instance method. When synchronized is used with a static method, a lock for the entire class is obtained. When synchronized is used with a non-static method, a lock for the particular object (that means instance) of the class is obtained. Since both methods are synchronized methods, you are not asked to explain what is a synchronized method. You are asked to tell the difference between instance and class method. Of course, your explanation to how synchronized keyword works doesn't hurt. And you may use this opportunity to show your knowledge scope.

Answer - 132 : - The Collections class has six methods to help out here: 1. unmodifiableCollection(Collection c) 2. unmodifiableList(List list) 3. unmodifiableMap(Map m) 4. unmodifiableSet(Set s) 5. unmodifiableSortedMap(SortedMap m) 6. unmodifiableSortedSet(SortedSet s) If you get an Iterator from one of these unmodifiable collections, when you call remove(), it will throw an UnsupportedOperationException.

Answer - 133 : - Sure. A private field or method or inner class belongs to its declared class and hides from its subclasses. There is no way for private stuff to have a runtime overloading or overriding (polymorphism) features.

Answer - 134 : - This is a classic question. Yes or No depends on how you look at Java. If you focus on the syntax of "extends" and compare with C++, you may answer 'No' and give explanation to support you. Or you may answer 'Yes'. Recommend you to say 'Yes'. Java DOES support multiple inheritance via interface implementation. Some people may not think in this way. Give explanation to support your point.

Answer - 135 : - Short answer: final - declares constant finally - relates with exception handling finalize - helps in garbage collection If asked to give details, explain: final field, final method, final class try/finally, try/catch/finally protected void finalize() in Object class

Answer - 136 : - There are three tools that can be used to protect application working within the scope of security policies set at remote sites. keytool -- used to manage keystores and certificates. jarsigner -- used to generate and verify JAR signatures. policytool -- used for managing policy files. There are three tools that help obtain, list and manage Kerberos tickets. kinit -- used to obtain Kerberos V5 tickets. tklist -- used to list entries in credential cache and key tab. ktab -- used to help manage entries in the key table.

Answer - 137 : - There is a method called arraycopy in the System class. You can do it: System.arraycopy(sourceArray, srcOffset, destinationArray, destOffset, numOfElements2Copy); When you use this method, the destinationArray will be filled with the elements of sourceArray at the length specified.

Answer - 138 : - Yes, you can. The source and destination arrays can be the same if you want to copy a subset of the array to another area within that array.

Answer - 139 : - Cloning an array invloves creating a new array of the same size and type and copying all the old elements into the new array. But such copy is called shallow copy or shallow clone because any changes to the object would be reflected in both arrays.

Answer - 140 : - When copying elements between different arrays, if the source or destination arguments are not arrays or their types are not compatible, an ArrayStoreException will be thrown.