Oracle Certification Associate 1Z0-808

From My Limbic Wiki

Links

Installation

Windows

<source lang="Shell"> C:\Program Files\Java </source>

  • Java Se Development Kit 8
    • Java FX SDK
    • Private JRE - Java Runtime Edition
    • Java Mission Control Tools

Can also be installed:

    • Development Tools
    • Source Code
    • Public JRE

Linux

<source lang="Shell"> sudo apt-get install oracle-java8-installer cd /usr/lib/jvm/java-8-oracle

  1. Java version

java -v

  1. Java Compiler

javac -version </source>

Basics

Main Method

<source lang="Java"> public static void main(String[] args]) </source>

Comments

<source lang="Java"> // Single Line Comment

/* Multi Line Comment

  • /

/** 

* Java Doc Comment
* @param
* @return 
*/

</source>

Import Conflicts

<source lang="Java"> import java.util.*; import java.sql.*;

// ==> in code = COMPILATION error Date date; </source>

Static Imports

It is not a good idea to do static imports a lot in a projet because it makes difficult to understand where the methods / constants come from

  • Static imports are for importing static members
  • Classic imports are for importing classes

it can be used for methods and constants for example <source lang="Java"> import static java.lang,Math.*;

// Instead of typing Math.min(1,2); we can just type min(1,2) // Because of the static import </source>

Primitives

It is not a good practice to use "l" instead of "L" while declaring long numbers because "l" looks like a "1" number so it can be confusing

Since Java 7 we can use "_" to makes number easier to read.

  • Can be anywhere except: beginning of literal, end of literal and right before or right after the decimal point.
  • Error: Illegal Underscore ==> the code does not compile
KeyWord Size Examples Smallest Data-Type
Boolean - true
Numbers without decimal points
byte 8-bits 1
short 16-bits 12 comment
int 32-bits 100 Default all numbers in Java
long 64 bits 12 Requires "L" letter to avoid compilation error, even when stored in long variable
float 32-bits 123.45 Requires letter "f" following the numbers
double 64-bits 123.45

Default all primitives or all that similar types.

Can use "d" / "D" letter to specify

Can convert a Float to Double

char 16-bits 'a'

Octal Numbers

Octal Numbers are numbers from 0 to 7. They can be used in java as

<source lang="Java"> // Valid int octalNumber = 07;

// Invalid - Number is too large, Compilation Error ! int octalNumber = 08; // it is not an octal number

// Valid - BUT coding standards prohibit use of octal literals, as they may be easily confused with decimal literals int octalNumber = 010 // 8 in decimal;

// Valid int declaration int octalNumber = 022; // 18 in decimal

// Valid int declaration int octalNumber = 8;

System.out.println(octalNumber); // print it's int value // Integer to octal String Integer.toOctalString();

</source>

Hexadecimal

Hexadecimals are numbers from 0 to 9 and letters from A to F <source lang="Java"> // Valid int firstHexNumber = 0xF; // 15 in decimal int secondHexNumber = 0x1E; // 30 in decimal

// Print the decimal value System.out.println(firstHexNumber); // print the Hexadecimal value: Integer.toHexString(firstHexNumber);

// p indicates hexadecimal floating point number double hexPi = 0x1.91eb851eb851fp1 </source>

Binary

<source lang="Java"> // Valid int firstBinary = 0xF; // 15 in decimal int secondBinary= 0x1E; // 30 in decimal

// Print the decimal value System.out.println(firstBinary ); // print the Hexadecimal value: Integer.toBinaryString(firstHexNumber); </source>

Scientific Notation

<source lang="Java"> // Both are valid and compile double scientificNotation = 5.000125E3 // in double 5000.125 double scientificNotation = 5.000125E03 // in double 5000.125 </source>

Chars

<source lang="Java"> char ch = 'a'; char ch1 = '1'; // it is still a char char uniChar = '\u03A9'; // upper case greek omega character char romanNumber= '\u216C'; // roman 50 number </source>

Booleans

<source lang="Java"> boolean booleanTrue = true; System.out.println(booleanTrue); // the ouput is "true"; </source>

Variables

Declaring and initializing

Allowed Characters in variables names: letter digit, dollar sign, underscore.

Declare and or initialize multiple variables on the same line is OK but not a good practice

  • with coma speration: If some are declared only and other initialized, it will compile !
  • with semi colomn separation, but on the same line

<source lang="Java"> int myVariable; // Declaration

// compilation error - Variable might not have been initialized System.out.println(myVariable);

myVariable = 10; // Initialization

//int i3; i4; // does not compile - they are not the same statement

// Java is case sensitive, but it can make the code really hard to understand char char; // does not compile char Char; // compile - not a good practice char cHar; // compile - not a good practice

// Illegal examples

double 3Dpoint; // Variable name cannot start with number double my@Street; // @ is not a letter digit, dollar sign or underscore </source>

About Initialization

<source lang="Java"> public class DefaultInitialization{ 

   static boolean myBoolean;
   static byte myByte;
   static short myShort;
   static int myInt;
   static long myLong;
   static float myFloat;
   static double myDouble;
   static char myChar;

   public static void main(String[] args){
       int localInt;

// System.out.println("localInt= " + localInt); // compilation error - Variable might not have been initialized 

       System.out.println("myBoolean= " + myBoolean); // false
       System.out.println("myByte= " + myByte); // 0
       System.out.println("myShort= " + myShort); // 0
       System.out.println("myInt= " + myInt); // 0
       System.out.println("myLong= " + myLong); // 0
       System.out.println("myFloat= " + myFloat); // 0.0
       System.out.println("myDouble= " + myDouble); // 0.0
       System.out.println("myChar= " + myChar); // 
   }

}

</source>

Scope

<source lang="Java"> public class VariableScope { 

   static int globalInt = 5; // global variable

   public static void main(String[] args) {
       int localInt = 10; // local variable

       {
           int microInt = 10; // local variable - can be only accessed in this curcly brackets block
           {
               {
                   // int microInt = 20; // will not compile because is defined in the parent block and in the same scope
               }
           }
       }
       System.out.println(microInt); // compilation error

       int microInt = 30; // can be defined, because it has a different scope
   }

} </source>

Class

Any error in this order will be followed by a compilation error.

  1. Package Declaration
  2. Import Statements
  3. Class Declaration
  4. Field Declarations
  5. Method Declarations

Null

A Null object will print "null" with a sout. But if we try to use the value to do anything, it will return <source lang="Java"> Java.lang.NullPointerException // then a stacktrace </source>

Exam Tips

  • Accolades mal placées
  • E scientifique remplacé par un F
  • Declare and or initialize multiple variables on the same line is OK but not a good practice
    • with coma speration: If some are declared only and other initialized, it will compile !
    • with semi colomn separation, but on the same line
Retrieved from "http://mylimbicwiki.fr/index.php?title=Oracle_Certification_Associate_1Z0-808&oldid=1453"