How do you create a read-only collection?

Java Interview Questions and Answers (part 1)

(Continued from previous question...)

147. How do you create a read-only collection?

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.

(Continued on next question...)

Other Interview Questions

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• Can you have virtual functions in Java?
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• How could Java classes direct program messages to the system console, but error messages, say to a file?
• What's the difference between an interface and an abstract class?
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• What do you understand by Synchronization?
• What is Collection API?
• Is Iterator a Class or Interface? What is its use?
• What is similarities/difference between an Abstract class and Interface?
• How to define an Abstract class?
• How to define an Interface?
• If a class is located in a package, what do you need to change in the OS environment to be able to use it?
• How many methods in the Serializable interface?
• How many methods in the Externalizable interface?
• What is the difference between Serializalble and Externalizable interface?
• What is a transient variable?
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• How are Observer and Observable used?
• What is synchronization and why is it important?
• What are synchronized methods and synchronized statements?
• What are three ways in which a thread can enter the waiting state?
• Can a lock be acquired on a class?
• What's new with the stop(), suspend() and resume() methods in JDK 1.2?
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• What would you use to compare two String variables - the operator == or the method equals()?
• What is thread?
• What is multi-threading?
• How does multi-threading take place on a computer with a single CPU?
• How to create a thread in a program?
• Can Java object be locked down for exclusive use by a given thread?
• Can each Java object keep track of all the threads that want to exclusively access to it?
• Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?
• What invokes a thread's run() method?
• What is the purpose of the wait(), notify(), and notifyAll() methods?
• What are the high-level thread states?
• What is the difference between yielding and sleeping?
• What happens when a thread cannot acquire a lock on an object?
• What is the difference between Process and Thread?
• Can an inner class declared inside of a method access local variables of this method?
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• What modifiers may be used with an inner class that is a member of an outer class?
• If a method is declared as protected, where may the method be accessed?
• What is an Iterator interface?
• How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
• What's the main difference between a Vector and an ArrayList?
• What are wrapped classes?
• Does garbage collection guarantee that a program will not run out of memory?
• What is the difference between preemptive scheduling and time slicing?
• Name Component subclasses that support painting?
• What is a native method?
• How can you write a loop indefinitely?
• Can an anonymous class be declared as implementing an interface and extending a class?
• What is the purpose of finalization?
• When should the method invokeLater()be used?
• How many methods in Object class?
• How does Java handle integer overflows and underflows?
• What is the numeric promotion?
• Is the numeric promotion available in other plantform?
• What is the difference between the Boolean & operator and the && operator?
• When is the ArithmeticException throwQuestion: What is the GregorianCalendar class?
• What is the SimpleTimeZone class?
• How can a subclass call a method or a constructor defined in a superclass?
• What is the Properties class?
• What is the purpose of the Runtime class?
• What is the purpose of the System class?
• What is the purpose of the finally clause of a try-catch-finally statement?
• What is the Locale class?
• What is an abstract method?
• What is the difference between interface and abstract class?
• What is a static method?
• What is a protected method?
• What is the difference between a static and a non-static inner class?
• What is an object's lock and which object's have locks?
• When can an object reference be cast to an interface reference?
• What is the difference between a Window and a Frame?
• What is the difference between a Window and a Frame?
• Which package has light weight components?
• What are peerless components?
• What is the difference between the Font and FontMetrics classes?
• What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?
• What classes of exceptions may be caught by a catch clause?
• What is the difference between throw and throws keywords?
• If a class is declared without any access modifiers, where may the class be accessed?
• What is the Map interface?
• Does a class inherit the constructors of its superclass?
• Name primitive Java types.
• Which class should you use to obtain design information about an object?
• How can a GUI component handle its own events?
• How are the elements of a GridBagLayout organized?
• What advantage do Java's layout managers provide over traditional windowing systems?
• What are the problems faced by Java programmers who don't use layout managers?
• What is the difference between static and non-static variables?
• What is the difference between the paint() and repaint() methods?
• What is the purpose of the File class?
• Why would you use a synchronized block vs. synchronized method?
• What restrictions are placed on method overriding?
• What is casting?
• Explain the usage of the keyword transient?
• What class allows you to read objects directly from a stream?
• How are this() and super() used with constructors?
• How is it possible for two String objects with identical values not to be equal under the == operator? How are this() and super() used with constructors?
• What is an IO filter?
• What is the Set interface?
• How can you force garbage collection?
• What is the purpose of the enableEvents() method?
• What is the difference between the File and RandomAccessFile classes?
• What interface must an object implement before it can be written to a stream as an object?
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• What are the Object and Class classes used for?
• What is Serialization and deserialization?
• Explain the usage of Java packages.
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• What is design by contract?
• What are use cases?
• What is scalability and performance?
• What is the benefit of subclass?
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