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Yash edited this page Sep 29, 2016 · 23 revisions

Eclipse IDE for Java EE Developers:

Removing Startup WORK SPACE

  • From File: Go to specified location then Select and Remove work-spaces names which you what to delete.

Eclipse-Installation Path\configuration\.settings\org.eclipse.ui.ide.prefs [MAX_RECENT_WORKSPACES=7 RECENT_WORKSPACES=WORKSPACE1\nWORKSPACE2\nWORKSPACE3]

  • Through IDE: Windows → Preferences → General « Startup and Shutown « Workspaces → list of Recent WORK SPACE-Names are available, select one from it and click on [Remove] button.

Eclipse Tomcat Server Creation Problem

In Eclipse if you can't create another instance for Tomcat server of any version, then.

  1. Close Eclipse.
  2. from this location {workspace-directory}/.metadata/.plugins/org.eclipse.core.runtime/.settings delete the following two files: org.eclipse.wst.server.core.prefs org.eclipse.jst.server.tomcat.core.prefs
  3. Restart Eclipse

Select external Web Browser

Through IDE either you can select any of the listed browsers or you can create New by providing → Browser name and Installation location. Location: Windows → Preferences → General → Web Browser « use external web browser

Change Tomcat Title

In order to changed the title that appears on the top of the Tomcat-console.

Tomcat-Installation Path/bin/catalina.bat

:doStart « if "%TITLE%" == "" set TITLE=Chenge the title Tomcat

Show Line Numbers

  1. From File: From this file org.eclipse.ui.editors.prefs change property values to true. File Location → [work space.metadata.plugins\org.eclipse.core.runtime.settings\org.eclipse.ui.editors.prefs] & its Property values → lineNumberRuler=true showWhitespaceCharacters=true

  2. Through IDE Window → Preferences → General « Editors « Text Editors [Check/UN check] Show line Numbers.

CTRL + F10 then N - Show or Hide line Numbers

OpenJDK Downloads : 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. Basic, Refactoring Techniques

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 1.1security-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

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