Java Basics

Primitive Types

byte
char - 16 bit
short
int
long - 64 bit
boolean
float
double

Variables

• variable of primitive types holds value.
• variable of non-primitive types holds reference.

Variable Storage

• Static - static class variables
• Local  - primitives
• Dynamic - non-primitives

Parameters

• All the parameters are pass-by-value (since the variables can only be value or reference; for reference it is a copy of the reference). 
• There is no direct way change content of a primitive type with parameter (can wrap with array or object).

Class

Accessibility

public
private
protected - subclass and class from the same package.
package - member without any leading keyword get default package access.

• no C++ const method

• no ";" after class {}

Inheritance

• no C++ multiple inheritance

• Object is default base class if no base class is specified. Which is the root base class for all classes.
• super is used to initialize superclass.

import Person;
public class Student extends Person
{
   private String major;
   public Student(String name, String major)
   {
      super(name);
      this.major=major;
   }
} 

Static and Dynamic Binding

• virtual by default

 void a();  //C++==>  virtual void a();

Abstract Methods

abstract a();  //C++==> virtual void a()=0;

Call Superclass Version

super.a();     //C++==> baseName::a();

Final Methods

• Cannot be overriden in a subclass
  
  

final void a();

Exceptions

• Java exception class must be a subclass of the java.lang.Exception class (which is a subclass of java.lang.Throwable).
• C++ exception can be of any class.

Features of C++ does not exist in Java

• Preprocessor
• Enumeration Types
• Templates
• Operator Overloading
• Named types (typedef)
• Structs and unions
• const class function member.