Notes.md

JAVA Collections Notes

TreeMap

• Insertion order not preserved
• Duplicate keys not allowed
• Defaultsorting order:keys should be homogenous and comparable
• Customised Order:Need not be homogenous
• Null is not allowed

Concurrent Collection

• Synchronisation to prevent data consistency
• List and Linked list are not synchronised
• Collections have methods to make these synchronised :
• Collections.synchronizedList(ist);
• Collections.synchronizedMap(map);

Concurrenthashmap

• Provides ultimate concurrency
• More helpful in multithreading
• By default has 16 divisions called concurrency level ,do not change it
• It locks only a portion of code
• It is better than hash table and synchronised map
• Null not allowed
• Fail safe supports iteration and modification simultaneously

Copy on write ArrayList

• Read is done on main object and write on cloned object, this is how thread safety is achieved

Lambda

• Functional programming is achieved
• To write clean code
• To use parallel processing
• Function without any name, modifier or return type
• It can guess the value’s datatype

Functional Interface

• Interface contains only a single abstract method

Predicate

• It is a predefined functional interface
• Interface Predicate{ boolean test(T t); }

Generics

• Type checking at compile time
• We tell the compiler the datatype we are using and if a mistake is made a compile time error is asked to be raised
• Public class Data(T is the type parameter)
• Generic class and interfaces -[ ] Type parameter is only for generic classes, methods and constructors only

Restrictions with WildCards

• We cannot use them as type parameter in class level, I.e at the header Eg: public class Box<?>->This is not allowed
• Does not support multiple bounds eg:<? Extends Number &Runnable>
• No restrictions on Read operations
• When upper bound is used we cannot add anything
• But lower bound when used we can add elements
• You cannot add anything to a list of unknown type