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Java Primitives versus Objects

  • Java has two types of data types :

    • Primitive data type : int, boolean , double .
    • references like Integer , Double , String .

  • converting primitive type to reference is called autoboxing .

  • Choosing which of these type Depends on how much memory available to use and what default values to handle .

  • Wrapper classes are immutable .

Primitive size on memory :

- boolean 1 bit .
- byte 8 bits .
- short , char 16 bits .
- int , float 32 bits .
- double , long 64 bits .
  • Values depend from each JVM .

Reference types are on heap memory and slower to access with the following sizes :

- Boolean , Integer , Float , Short ... : 128 bits .
- Long , Double : 192 bits .

  • The size for array is a little different which occupies 64 bit multiplied by a percentage depending on the type and 128 bit static .

  • Running time of a java application depends on the hardware and the jvm and some circumanstances .

  • Primitives live on the stack and references lives on heap memory .

  • Primitives has an actual value as default but for references null is the default .

  • Generics and collections requires using references by default, furthermore the primitives are much faster .

Exceptions

What is an exception?

  • An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions.
  • When an error occurs an object is created with the error information about the error and the state of the program .
  • this process is called throwing an exception and is handled to the running system .
  • when the exception is thrown the compiler start looking for handler to this exception starting from the method where the exception was thrown .
  • if a block of code was found to handle that exception that is called catching the error and terminates the program .

The Catch or Specify Requirement

  • Valid java program must appropriatly use try and catch to handle exceptions .

Three types of exceptions :

1. checked exceptions : checked exception where we have to handle exceptions hence their will be terminating the program and all of it's tasks once an exception occurs .
- All exceptions are checked other than error and runtime exceptions and their sub classes.
- The only type of exception that the program can recover from.


2. Error : error throw the running process of the program for example IOError exception .

3. Runtime exception : this happens when a runtime , logical , mathmatical error occurs for example NullPointerException .

Scanning

  • Scanner : an objects of type useful for breaking down formatted input into tokens and translating individual tokens according to their data type.

Breaking Input into Tokens

  • a scanner uses white space to separate tokens
  • white space characters - blanks, tabs, and line terminators

Translating Individual Tokens

  • Scanner supports tokens for all of the Java language's primitive types with the exception of char.
  • Numeric values can use thousands separators.