Oracle Certification Associate 1Z0-808: Difference between revisions
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===Declaring and initializing=== | ===Declaring and initializing=== | ||
<div style="color:#2ACD37; font-weight: bold;"> | <div style="color:#2ACD37; font-weight: bold;"> | ||
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 | |||
</div> | </div> | ||
<source lang="Java"> | <source lang="Java"> |
Revision as of 19:01, 4 June 2020
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
- Java version
java -v
- 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
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 </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