Value In Brief
All You Need To Know Explained In Brief

Java for Android – Documentation and Code Snippets

Java programming languages

All you need to create Android app in Java.

Java Syntax

Primitive Data Types

Java Operators:

Java Code Snippets

Class Implementation

public class MyClass {

 public String mString;
 private int mInt;
 // More member variables

 // Constructor for Class
 public MyClass() {
 mString = Foo;
mInt = 10;
 }
 // More methods...
}

Methods

public int doIt() {
 return 0;
}
public int doIt(int a) {
 return a;
}
public int doIt(int a, int b) {
 return a+b;
}

Creating / Using an Instance

SomeObject a = new SomeObject();
a.getMemberVariable();
a.doIt();
a.doIt(1);
a.doIt(2,3);
Declaring Variables
double doubleVar = 1.0
doubleVar = 2.0
int intVar = 1;
String stringVar = Hey;
Boolean truth = true;

Variable Types

variable keyword sample values
int 1, 2, 500, 10000
float, double 1.5, 3.14, 578.234
boolean true, false
string “Abanoub”, “John”, “Samy”
ClassName Activity, TextView, .. etc

Control Flow

Boolean condition = true;
if (condition) {
} else {
}
int val = 5;
switch (val) {
 case 1:
 break;
 case 2:
 break;
 default:
 break;
}
for (int i = 0; i < 5; i++) {
}

String Quick Example

String personOne = "Ray";
String personTwo = "Brian";
String combinedString = personOne + ": Hello, " + personTwo + "!";
String tipString = "2499.00";
Int tipInt = Integer.parseInt(tipString);
double tipDouble = Double.parseDouble(tipString);

Array Quick Examples

String personOne = "Ray";
String personTwo = "Brian";
String [] array = {personOne, personTwo};
for(String person : array) {
 Log.d("person:", person);
}
String ray = array[0];

Dictionary Quick Examples

HashMap<String, String> map = new
HashMap<>();
map.put(personOne,Ray);
// updates old value if already exists
map.put(personOne,Brian);
map.put(personTwo,Darryl);
// remove value for key
map.remove(personOne);
// iterate through map
for(Map.Entry<String, String>
personEntry : map.entrySet()) {
Log.d(personEntry.getKey(),
personEntry.getValue());
}

Java Code Snippets / Code Samples for Android

How to get file from assets in Java on Android

//the function to get the file as a string
public String loadData(String inFile) {
 String tContents = "";
 try {
    InputStream stream = getAssets().open(inFile);
    int size = stream.available();
    byte[] buffer = new byte[size];
    stream.read(buffer);
    stream.close();
    tContents = new String(buffer);
 } catch (IOException e) {
    // Handle exceptions here
 }
 return tContents;
}
//calling the function
getFileFromAssets("test.html");
//or (any file)
getFileFromAssets("test.txt");

How to copy text to clipboard on Android in Java

//initialize the button & editText in OnCreate()
Button copyBtn = findViewById(R.id.copyBtn);
EditText toCopy = findViewById(R.id.etCopy);

//when you click the copy-button this methon/function is fired
copyBtn.setOnClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View v) {
     //the copy2clipboard function called with the text of the editText
     copy2Clipboard(toCopy.getText().toString());
  }
});
//the function to copy any text passed in
void copy2Clipboard(CharSequence text){
  ClipboardManager clipboard = (ClipboardManager) getSystemService(Context.CLIPBOARD_SERVICE);
  ClipData clip = ClipData.newPlainText("copy text", text);
  if (clipboard != null){
     clipboard.setPrimaryClip(clip);
  }
  Toast.makeText(this," text copied", Toast.LENGTH_LONG).show();
}

Get the first n characters of a string

//s -> the string
//n -> the n of characters
//upToNCharacters -> the final string
String upToNCharacters = s.substring(0, Math.min(s.length(), n));

How to save file on Android in Java

//add those permissions to manifest.xml
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

//call the function
saveFile(getApplicationContext(), "filename", "the content of the file itself");

//you can use "this" instead of "getApplicationContext()"
saveFile(this, "anotherFileName", "content of the file 2");

//saveFile function
public void saveFile(Context mcoContext,String sFileName, String sBody){

 File file = new File(mcoContext.getFilesDir(),"CVApp");

 if(!file.exists()){
    file.mkdir();
 }

 try{
    File gpxfile = new File(file, sFileName);
    FileWriter writer = new FileWriter(gpxfile);
    writer.append(sBody);
    writer.flush();
    writer.close();
 }catch (Exception e){
    e.printStackTrace();
 }
}

How to implement merge sort algorithm in Java

package Sorts;

import static Sorts.SortUtils.print;

class MergeSort implements SortAlgorithm {

    @Override
    @SuppressWarnings("unchecked")
    public <T extends Comparable<T>> T[] sort(T[] unsorted) {
        T[] tmp = (T[]) new Comparable[unsorted.length];
        doSort(unsorted, tmp, 0, unsorted.length - 1);
        return unsorted;
    }

    private  static <T extends Comparable<T>> void doSort(T[] arr, T[] temp, int left, int right) {
        if (left < right) {
            int mid = left + (right - left) / 2;
            doSort(arr, temp, left, mid);
            doSort(arr,  temp,mid + 1, right);
            merge(arr, temp, left, mid, right);
        }
   }

    private static <T extends Comparable<T>> void merge(T[] arr, T[] temp, int left, int mid, int right) {
        System.arraycopy(arr, left, temp, left, right - left + 1);


        int i= left;
        int j = mid + 1;
        int k = left;

        while (i <= mid && j <= right) {
            if (temp[i].compareTo(temp[j]) <= 0) {
                arr[k++] = temp[i++];
            }
            else {
                arr[k++] = temp[j++];
            }
        }

        while (i <= mid) {
            arr[k++] = temp[i++];
        }

	while (j <= right) {
	    arr[k++] = temp[j++];
	}
    }

    // Driver program
    public static void main(String[] args) {

        // Integer Input
        Integer[] arr = {10, 9, 8, 4, 5, 6, 13, 55, 72, 86, 100, 123, 7, 3, 2, 1};
        MergeSort mergeSort = new MergeSort();
        mergeSort.sort(arr);

        // Output => 1	   4  	 6	9	12	23	54	78	231
        print(arr);

        // String Inpu
        // String[] stringArray = {"c", "a", "e", "b","d"};
        // mergeSort.sort(stringArray);
        // Output => a	b	c	d	e
        // print(stringArray);
    }
}

Finally

This documentation and code snippets will be updated monthly.