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JVM Memory Areas and Scope
new Object() {
public void a() {
/*code*/
}
}.a();
Check .class
files. weather it generates anonymous inner class.
-> If you are creating inner class it generates 2.class files.
An inner class is a class that is defined inside another class. Why would you want to do that? There are three reasons:
Inner class methods can access the data from the scope in which they are defined—including the data that would otherwise be private. Inner classes can be hidden from other classes in the same package. Anonymous inner classes are handy when you want to define callbacks without writing a lot of code.
Anonymous inner class
public class Gui {
LineGraph graph = new LineGraph() {
// extra functionality here.
};
}
Named inner class
public class Gui {
MyLineGraph graph = new MyLineGraph();
private class MyLineGraph extends LineGraph {
// extra functionality here.
}
}
One advantage of anonymous inner classes is that no one can ever use it anywhere else
In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behavior.
Method signature: It consists of method name and parameter list (number/type/order of the parameters). methodName(parametersList y)
. An instance method in a subclass with the same signature
and return type
as an instance method in the super-class overrides the super-class's method.
Java OOP concepts
Class - Collection of a common features of a group of object [static/instance Fields, blocks and Methods]
Object - Instance of a class (instance fields)
Abstraction - Process of hiding complex info and providing required info like API, Marker Interfaces ...
Encapsulation(Security) - Class Binding up with data members(fields) and member functions.
Inheritance (Reusability by placing common code in single class)
1. Multilevel - {A -> B -> C} 2. Multiple - Diamond problem {A <- (B) -> C} [Java not supports] 3. Cyclic {A <-> B} [Java not supports]
* Is-A Relation - Class A extends B
* Hash-A Relation - Class A { B obj = new B(); } - (Composition/Aggregation)
Polymorphism (Flexibility) 1. Compile-Time Overloading 2. Runtime Overriding [Greek - "many forms"]
int[] arr = {1,2,3}; int arrLength = arr.length; // Fixed length of sequential blocks to hold same data type
String str = "Yash"; int strLength = str.length(); // Immutable Object value can't be changed.
List<?> collections = new ArrayList<String>(); int collectionGroupSize = collections.size();
Map<?, ?> mapEntry = new HashMap<String, String>();
Set<?> keySet = mapEntry.keySet(); // Set of Key's
Set<?> entrySet = mapEntry.entrySet(); // Set of Entries [Key, Value]
// Immutable Objects once created they can't be modified. final class Integer/String/Employee
Integer val = Integer.valueOf("100"); String str2 = String.valueOf(100); // Immutable classes
final class Employee { // All Wrapper classes, java.util.UUID, java.io.File ...
private final String empName; // Field as Final(values can be assigned only once) Only getter functions.
public Employee(String name) { this.empName = name; }
}
Native Java Code for Hashtable.h
, Hashtable.cpp
SQL API
.
You can check your current JDK and JRE versions on your command prompt respectively,
- JDK
javac -version [C:\Program Files\Java\jdk1.8.0_121\bin]
o/p:javac 1.8.0_121
- JRE
java -version
[C:\Program Files\Java\jdk1.8.0_121\bin]
o/P:java version "1.8.0_102"
JAVA_HOME - Must be set to JDK otherwise maven projects leads to compilation error. [ERROR] No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK?
C:\Softwares\OpenJDK\
, 7-zip
Fatal error compiling: invalid target release: JRE and JDK must be of same version
1.8.0.XXX
Disable TLS 1.0 and 1.1
security-libs/javax.net.ssl
: TLS 1.0 and 1.1 are versions of the TLS protocol that are no longer considered secure and have been superseded by more secure and modern versions (TLS 1.2 and 1.3).
Core Java
-
Java Programming Language Basics
- Object, Class, Encapsulation, Interface, Inheritance, Polymorphism (Method Overloading, Overriding)
- JVM Architecture, Memory Areas
- JVM Class Loader SubSystem
- Core Java Interview Questions & Programs
- Interview Concepts
Stack Posts
- Comparable vs Comparator
- Collections and Arrays
-
String, StringBuffer, and StringBuilder
- String reverse
- Remove single char
- File data to String
- Unicode equality check Spacing entities
- split(String regex, int limit)
- Longest String of an array
-
Object Serialization
- Interface's Serializable vs Externalizable
- Transient Keyword
-
implements Runnable
vsextends Thread
- JSON
- Files,
Logging API
- Append text to Existing file
- Counting number of words in a file
- Properties
- Properties with reference key