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→Eclipse shortcuts
===With apt===
===With apt===
<nowiki>sudo apt-add-repository ppa:webupd8team/java
<nowiki>sudo apt-add-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java8-installer</nowiki>
Also ensure your JAVA_HOME variable has been set to:
Also ensure your JAVA_HOME variable has been set to:
</syntaxhighlight>
</syntaxhighlight>
=== CopyOnWriteArrayList ===
===CopyOnWriteArrayList===
Expensive write, fast concurrent read, synchronized writes, free reads. <syntaxhighlight lang="java">
Expensive write, fast concurrent read, synchronized writes, free reads. <syntaxhighlight lang="java">
import java.utils.List;
import java.utils.List;
}
}
}
}
</syntaxhighlight><br />
</syntaxhighlight>
== Java tips ==
=== Static imports ===
<syntaxhighlight lang="java">
import static java.lang.System.out;
import static java.util.Collections.*;
out.println("System.out.printl System not needed");
sort(new ArrayList<String>());
</syntaxhighlight>
=== Blocks ===
<syntaxhighlight lang="java">
pubublic class BlocksRunner {
public static void main(String[] args){
{
int i;
System.out.println("i can be accessed here: " + i);
}
System.out.println("i can not be accessed here")
}
}
</syntaxhighlight>
=== equals and hashCode methods from an object ===
2 objects only obj.equals if they are the same object, but equals can be overriden (generate hashcode and equals)
Hash function should return the same value if 2 objects are equal
=== Access modifiers ===
public: accessible every where.
protected: accessible in same package or subclasses.
(default): only inside the class or package.
private: only inside the class.
=== non access modifier ===
==== final ====
final classes can not be extended.
final methods can not be overridden.
final variable can not change (Constants).
final argument can not be changed.
==== static ====
static class variables are common to all class instances.
static methods can be called from class, no need for instance, inside static methods instance variables or methods are not accessible.
==== Constants ====
public static final
==== Enums ====
like: java.time.Month, java.time.DayOfWeek<syntaxhighlight lang="java">
enum Season {
WINTER, SPRING, SUMMER, FALL;
// to store in db
private int value;
WINTER(1), SPRING(2), SUMMER(3), FALL(4);
private Season(int value){
this.value = value;
}
}
public class EnumRunner{
public static void main(String[] args){
Season season = Season.WINTER;
Season season1 = Season.valueOf("WINTER");
System.out.print(season1);
System.out.print(Season.SPRING.ordinal());
System.out.print(Season.SPRING.getValue());
System.out.print(Arrays.toString(Season.values()));
}
}
</syntaxhighlight>
== Sort strings ==
<syntaxhighlight lang="java">
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Comparator;
class LengthComparator implements Comparator<String> {
@Override
public int compare(String str1, String str2){
return Integer.compare(str1.length(), str2.length());
}
}
public class AnonymousClassRunner{
public static void main(String args){
List<String> animals = new ArrayList<String>(List.of("Ant", "Cat", "Ball", "Elephant"));
// Collections.sort(animals); //Alphabetical order
Collections.sort(animals, new LengthComparator()); //Length order
System.out.println(animals);
}
}
</syntaxhighlight>
==Eclipse shortcuts==
==Eclipse shortcuts==
Ctrl + Space → Autocomplete.<br />
Ctrl + Space → Autocomplete.<br />