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‎Java Assertions.txt

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Java Assertions
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‎Java Testing With JUnit.txt

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JUnit
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‎Java Version Specific.txt

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It is a generic type that is parametrized with an unbounded ( <?> ) or bounded ( <? extends T> ot <? super T> ) wildcard type. A wildcard type basically tells us that the type parameter can be any type.
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4. What is Autoboxing/unboxing and what are its advantages/pitfalls?
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4. What is Autoboxing/unboxing?
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Autoboxing is automatic casting of variables of primitive types to corresponding wrapper class. Unboxing is the inverted cast.
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Useful to reduce the amount of code to be written. Pitfalls: can be unintentionally slow if used in a loop. Also care has to be taken with cached values. (e.g. a pool of Integers from -128 to +127)
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5. Enables to associate additional data with enum constants
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6. What are Annotations and which predefined by the language specification does one know (@Deprecated, @Override, @SuppressWarnings)
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From http://docs.oracle.com/javase/tutorial/java/javaOO/annotations.html
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Annotations provide data about a program that is not part of the program itself. They have no direct effect on the operation of the code they annotate. Annotations can be applied to a program's declarations of classes, fields, methods, and other program elements.
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@Deprecated -- to inform that the method is deprecated
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@Override -- to inform that this method has to override a method in a superclass. Helps to find errors.
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@SuppressWarnings -- to suppress warnings. E.g. warnings generated when doing potentially unsafe cast
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16. Annotation retentions policies and why they are in place?
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TODO: ...
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The retention policies specify how long annotations are to retained.
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CLASS: Annotations are to be recorded in the class file by the compiler but need not be retained by the VM at run time. Useful for bytecode postprocessing. Cannot be inspected at run-time with reflection getAnnotations
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RUNTIME: Annotations are to be recorded in the class file by the compiler and retained by the VM at run time, so they may be read reflectively. (@Deprecated)
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SOURCE: Annotations are to be discarded by the compiler. (Example: @Override, @SuppressWarnings)
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17. Suppose you would like to reuse a class in different contexts would you use annotations or external configuration? (i.e. annotation introduce dependencies).
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Good discussion of this question can be found here
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http://javidjamae.com/2006/11/19/annotations-vs-xml/
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Java 7 specifics
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1. Try with resource
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The try-with-resources statement is a try statement that declares one or more resources. A resource is an object that must be closed after the program is finished with it. The try-with-resources statement ensures that each resource is closed at the end of the statement. Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.
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Example
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static String readFirstLineFromFile(String path) throws IOException {
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try (BufferedReader br =
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new BufferedReader(new FileReader(path))) {
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return br.readLine();
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}
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}
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2. Diamond operator
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In Java 7 writing the type parameters twice is no longer needed.
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Example:
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Instead of writing HashMap<String, Integer> hm = new HashMap<String,Integer>();
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one can just write HashMap<String, Integer> hm = new HashMap<>();
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The latter is now preferable
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3. Better exception catching
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In Java 7 the same processing can be performed for a whole list of exceptions:
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try {
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...
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} catch (ExceptionType1 | ExceptionType2 | ExceptionType3 ex){
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// do some processing
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}
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Note that these exceptions cannot belong to the same hierarchy (none is subclass or superclass of the other)
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4. Strings in switch statement
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String dayOfWeek = "Mon";
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switch (dayOfWeek.toLowerCase()) {
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case "mon" :
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//do something
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break;
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case "tue" :
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//do something
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break;
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...
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default :
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//do something
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break;
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}
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5. Numeric literals with underscores
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From http://docs.oracle.com/javase/7/docs/technotes/guides/language/underscores-literals.html
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In Java SE 7 and later, any number of underscore characters (_) can appear anywhere between digits in a numerical literal. This feature enables you, for example, to separate groups of digits in numeric literals, which can improve the readability of your code
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long creditCardNumber = 1234_5678_9012_3456L;
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long socialSecurityNumber = 999_99_9999L;
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float pi = 3.14_15F;
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6. New I/O.
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Lots of stuff here. More info cat be found at
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http://docs.oracle.com/javase/tutorial/essential/io/fileio.html
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http://www.drdobbs.com/jvm/java-se-7-new-file-io/231600403
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7. Fork/Join framework
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The fork / join framework is an implementation of the ExecutorService interface that helps you take advantage of multiple processors. It is designed for work that can be broken into smaller pieces recursively.
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Example can be found here
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http://docs.oracle.com/javase/tutorial/essential/concurrency/forkjoin.html

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