Android Studio lock unlock file make read only or writable

        // get max end min values of int in Java example 4 bytes (32 bits) PC architecture
	System.out.println(Integer.MAX_VALUE); // 2147483647
	System.out.println(Integer.MIN_VALUE); // -2147483648


// members variable
private int mProgress = 10;

//integer to string java
int myInteger = 8;
String myString = Integer.toString(myInteger);

// a final variable can only be initialized once
static final int NUM_PARTICLES = 15;

 for (int i = 0; i < NUM_PARTICLES ; i++) { 
// do something
}

// int as return value of function
public int getCount() {
return 5;
}

// int as a parametr of function
public float getFloatFromInt(int i) {
float fRet = (float) i;
 return fRet;
}

//array of int
int[] anArray;              // declares an array of integers
          anArray = new int[2];      // allocates memory for 2 integers
          anArray[0] = 100; // initialize first element
          anArray[1] = 200; // initialize second element

for (int i = 0; i < anArray.length; i++) {
// print out values from anArray
System.out.println("Index: " + i);
System.out.println("Value: " + anArray[i]); 
}

    String[] source = {"Hello","world","by","Android"};
    
    String[] destination = new String[source.length];
   
    System.arraycopy(source, 0, destination, 0, source.length);

// get handle
Button myButton;
myButton = (Button)findViewById(R.id.idMyButton);
//set focus
myButton.requestFocus();
// set background image
myButton.setBackgroundResource(R.drawable.backImage);
// or
myButton.setBackgroundDrawable(getResources().getDrawable( R.drawable.someImage));

// set visibility
myButton.setVisibility(View.INVISIBLE); // VISIBLE

///////// SET LISTENER
       Button myButton =(Button)findViewById(R.id.button1);
        myButton.setOnClickListener(new Button.OnClickListener() {
            public void onClick(View v) {
                Toast.makeText(getApplicationContext(), "AHOJ",
                    Toast.LENGTH_LONG).show();
            }
        });	

// or set onClickListener
 myButton.setOnClickListener(myListener);
//end onCreate .....
   private OnClickListener myListener = new OnClickListener() {
        public void onClick(View v) {

        }
   }

 Display display = getWindowManager().getDefaultDisplay();
int nWidth = display.getWidth();
int nHeight = display.getHeight();

          DisplayMetrics metrics = new DisplayMetrics();
            getWindowManager().getDefaultDisplay().getMetrics(metrics);
            //get density per inch for example: 120 , 160 , 240
            mXDpi = metrics.xdpi; // 160 The exact physical pixels per inch of the screen in the X dimension. 
            mYDpi = metrics.ydpi;

// density
int nDensity = metrics.densityDpi; // 160 screen density expressed as dots-per-inch

          float  mMetersToPixelsX = mXDpi / 0.0254f; // 1 inch == 0.0254 metre
          float  mMetersToPixelsY = mYDpi / 0.0254f;
          
// Resolution
// The total number of physical pixels on a screen.
int wPix = metrics.widthPixels; // 320 The absolute width of the display in pixels.
int hPix = metrics.heightPixels; // 480 The absolute height of the display in pixels.
int nWidthDisplay = (wPix < hPix)? wPix : hPix;

float nWidthScreenInInch = wPix / mXDpi; //320 / 160 == 2.0 in inch.
float nHeightScreenInInch = hPix / mYDpi; //480 / 160 == 3.0 in inch.

// for example:
// density 120 per inch
//width 320 pix / 120 dpi == width 2.66 inch
//height 480 pix / 120 dpi == height 4.0 inch 

// density 240 per inch
//width 320 pix / 240 dpi == width 1.33 inch
//height 480 pix / 240 dpi == height 2.0 inch