public void changesong(View view)
{
    setContentView(R.layout.playlist);
            Intent i = new Intent(getApplicationContext(), PlayListActivity.class);
            startActivity(i);


}

Intent i = new Intent(your_present_class.this, PlayListActivity.class);

Intent i = new Intent(this, PlayListActivity.class);

<activity android:name = ".PlayListActivity" />

Intent i = new Intent(getApplicationContext(), PlayListActivity.class);
startActivity(i);

Intent i = new Intent(this, PlayListActivity.class);

<activity android:name = ".PlayListActivity" />