Android Studio formatting code Ctrl + Alt + L

Terms Screen size, density, density independent pixel, resolution as a picture - pictogram.


Test your knowledge
Q: How to find out the phone screen size?
A: (By length of display diagonale in inch -  Not to measure a diagonal of device!!!)

Q: What resolution has 720 x 1280 display?
A: (921600 pixels)

Q: What does it mean "240 dpi" screen density?
A: (Display have density 240 x 240  dots - "Tri-color LED etc." - per every physical (real) square inch. If you have icon 240x240 pixels, this will just occupy an area of one square inch on the display.)

Q: Phone have screen density 240 dpi. Image for 160 dpi screen density have size 128x 128 pixels. What will be the size of the image for 240 dpi screen density?
A: (Calculate the virtual pixels size.   128 * (240/160)  =  192.  You have to resize image to new size 192 x 192 physical pixels and put into folder drawable-hdpi (high) ~240dpi  for phone with screen density 240 dpi. ) or use density independend pixels 128dp x 128dp.

 

 

If you have trouble with compilation of new project after you make a update of android development tools you can go back to old version of the tools.

• 
  
  
  
  • Open Help > About Eclipse... use the menu > About...
  
  
  • Click the "Installation Details" button.
  
  
  • Select the "Installation History" tab.
  
  
  • Select one of the previous configurations.
  
  
  • Click the "Revert" button at the bottom.
  
  
  
  

Generate random number Android Java example source code.

		Random rand = new Random();
		int i = rand.nextInt() % 256; // range -255  +255
		System.out.print(i + "

"); // -184
		i = Math.abs(rand.nextInt() % 12); // range 0  +11
		System.out.print(i); // 7

// Math.random() start with 0.  e.g. 0.35981234 
int nRan = (int) (Math.random()*10); // 0 - 10

// nextDouble(), nextFloat(), nextInt(), nextLong() returns 0 - 10
import java.util.Random;´

Random r = new Random();
int nRan = r.nextInt(); // 0 - 10
double dRan = r.nextDouble() * 10; // e.g. 7.496285271597397

nextDouble – return 0 - 1
nextFloat – same as double
nextInt –  -2147483648  +2147483647
nextLong –  -922337203685775808  +9223372036854775807
nextGaussian –  0.0 aberation 1.0.

Map TreeMap sorted by value Java Android example.

MainClass.java

import java.util.Comparator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.SortedSet;
import java.util.TreeMap;
import java.util.TreeSet;

public class MainClass {
	public static void main(String[] arg) {

		// english;germany dictionary
		String[] arrayOfString = { "one;eine", "two;zwei", "three;drei",
				"four;vier" };

		Map<String, String> map = new TreeMap<String, String>();

		for (String s : arrayOfString) {
			String[] array = s.split(";");
			String sKey = "", sValue = "";
			if (array.length > 1) {
				sKey = array[0];
				sValue = array[1];
				map.put(sKey, sValue);
			}
		}
		for (Entry<String, String> entry: mapSortedByValues(map)) {
		    System.out.println(entry.getKey() + " = " + entry.getValue());
		}
	}

	static <K, V extends Comparable<? super V>> SortedSet<Map.Entry<K, V>> mapSortedByValues(
			Map<K, V> map) {
		SortedSet<Map.Entry<K, V>> sortedSetOfEntries = new TreeSet<Map.Entry<K, V>>(
				new Comparator<Map.Entry<K, V>>() {
					@Override
					public int compare(Map.Entry<K, V> entry_1, Map.Entry<K, V> entry_2) {
						int res = entry_1.getValue().compareTo(entry_2.getValue());
						return res != 0 ? res : 1; 
						// return entry_1.getValue().compareTo(entry_2.getValue());							
					}
				});
		sortedSetOfEntries.addAll(map.entrySet());
		return sortedSetOfEntries;
	}
}
/*
three = drei
one = eine
four = vier
two = zwei
 */

Integer, Float, String, List passed as reference in JAVA example source code:

// List passed as reference JAVA
List<Integer>list = new ArrayList<Integer>();

public void fc (List<Integer>listRef){
listRef.add(7);
listRef.add(5);
}
fc(list); // 7, 5 


// String passed as reference JAVA
	public void mutate(AtomicReference<Object> ref) { ref.set("Goodbye"); }

		AtomicReference<Object> ref = new AtomicReference<Object>("Hello");
		mutate(ref);
		System.out.println(ref.get()); //Goodbye!
             String s = (String) ref.get();


// Integer passed as reference JAVA
	private static void mutate(AtomicReference<Object> ref) { ref.set(7); }

	//public static void main(String[] arg) {
		AtomicReference<Object> ref = new AtomicReference<Object>(5);
		mutate(ref);
		System.out.println(ref.get()); // 7
int n = (Integer) ref.get();


// Float passed as reference JAVA
	private static void mutate(AtomicReference<Object> ref) { ref.set(14.8f); }

	//public static void main(String[] arg) {
		AtomicReference<Object> ref = new AtomicReference<Object>(12.1f);
		mutate(ref);
		float f = (Float) ref.get();
		System.out.println(f); //14.8