Chapter 13 - Java

Being one of the most successful languages in the history, there are a lot of language details to learn in Java. For example, there are many de-facto OOP concepts, such as inheritance, override vs overload, etc. You certainly should understand abstract, final, default, etc. as well. Java collection framework has a lot to test as well.

Examples

13.1 Private Constructor

If a class’s constructor is private, that class can only be inherited by inner classes.

13.2 Return from Finally

Yes, the finally block will still execute. The finally block will only be skipped if the thread or JVM is killed.

13.3 Final, etc.

• final means either the variable, field cannnot be modified after initialization or the class cannot be inherited.
• finally means the block will always be executed after try and/or catch.
• finalize is called by GC when there is no more reference(s) and collection happens.

13.4 Generics vs Templates

Java generics relies on type erasure, thus, it is only a syntax sugar. C++ templates form a glorified macro set. Each type will be generated into a new copy of the template code by the compiler.

13.5 TreeMap, HashMap, LinkedHashMap

• HashMap: the most basic key-value mapping, with O(1) insertion and lookup speed, do not preserve order;
• TreeMap: use red-black tree, with O(logn) insertion and lookup speed, preserve order;
• LinkedHashMap: O(1) insertion and lookup speed, preserve order by insertion order, can use to implement LRU cache.

13.6 Object Reflection

Reflection can be used to dynamically get meta-information about classes and objects at runtime.

13.7 Lambda Expressions

Use filter, map and reduce.

13.8 Lambda Random

Iterate through each element, use a 50% probability to decide whether to include it in the result.