title: get the size of data partition by coding
body: <p>i have test code using :</p>
  
  <pre><code>  $ adb -s emulator-5554 shell
  
     # df
     df
   /dev: 47084K total, 0K used, 47084K available (block size 4096)
  /sqlite_stmt_journals: 4096K total, 0K used, 4096K available (block size  4096)
  /system: 73600K total, 73600K used, 0K available (block size 4096)
  /data: 65536K total, 18464K used, 47072K available (block size 4096)
  /cache: 65536K total, 1156K used, 64380K available (block size 4096)
  </code></pre>
  
  <p>you see the data have total 65536k and so on,my question is how to get the size by coding?if i need root right?can you give me some advice?</p>