Strings and the R File
Strings (res/values/strings.xml)
The string @string/app_name in the AndroidManifest.xml can be found from the file strings.xml as below. Other than using an id such as app_name in a layout file to find a string, the developers can simply replace it by the string “Database Example.”

SQLiteDemo/app/src/main/res/values/strings.xml 
<?xml version="1.0" encoding="utf-8"?>
<resources>
  <string name="app_name">Database Example</string>
</resources>

The R File (com/example/wenchen/sqlitedemo/R.java)
The code below shows the contents of the generated file R.java, which is no longer generated by the Android Studio. There are two ways to refer the resources specified in the directory res/:

generated/source/r/debug/com/example/wenchen/sqlitedemo/R.java 
/* AUTO-GENERATED FILE.  DO NOT MODIFY.
 *
 * This class was automatically generated by the
 * aapt tool from the resource data it found.  It
 * should not be modified by hand.
 */

package com.wenchen.SQLiteDemo;

public final class R {
  public static final class attr {
  }
  public static final class drawable {
    public static final int icon=0x7f020000;
  }
  public static final class id {
    public static final int add=0x7f050001;
    public static final int delete=0x7f050002;
    public static final int group=0x7f050000;
  }
  public static final class layout {
    public static final int main=0x7f030000;
  }
  public static final class string {
    public static final int app_name=0x7f040001;
    public static final int hello=0x7f040000;
  }
}




      I was playing chess with my friend and he said,    
      “Let’s make this interesting.” So we stopped playing chess.    
      — Matt Kirshen