A set is an Interface that provides an un-ordered collection of unique objects (does not contain duplicate values). In provides three general purpose implementations in Java.
HashSet stores its elements in a HashTable and does not guarantee of any type of ordering in iteration.
TreeSet orders its elements on the basis of their values.
It orders its elements on the basis of order in which they were inserted in the set.
A List is an ordered and indexed collection that can contain duplicate values. List allows null elements. It provides three general purpose implementations.
ArrayList is more general purpose and provides random access with index. ArrayList is an expendable array of values or objects. If you need to access elements frequently by using index, ArrayList provides faster access if you know index. ArrayList represents an automatic re-sizeable array and used in place of array.
LinkedList is more suitable for frequently adding and removing elements from List. LinkedList also implements Deque interface, which provides first in first out operations.
Vector is synchronized and thread safe in nature.
A Map interface provides key-value pairs. Maps can not contain duplicate keys and one key can be mapped to atmost one element. In Java Map interface provides three general purpose implementations.
HashMap does not guarantee that the order of the objects will remain the same over the time.
JSON is a minimal, readable format for structuring data.
Features of JSON:
- It is light-weight
- It is language independent
- Easy to read and write
- Text based, human readable data exchange format
SQL injection is a technique where malicious users can inject SQL commands into an SQL statement, via web page input. Injected SQL commands can alter SQL statement and compromise the security of a web application. A SQL injection attack can occur when a web application utilises user-supplied data without proper validation or encoding as part of a command or query.
- filtering for rows;
- selecting specific columns;
- re-ordering rows;
- adding new columns;
- summarizing data.
Cross-Site Request Forgery (CSRF) is a type of attack that occurs when a malicious Web site, email, blog, instant message, or program causes a user’s Web browser to perform an unwanted action on a trusted site for which the user is currently authenticated.
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