How to align a view to the top of a RelativeLayout in Android

activity_main.xml 
 <RelativeLayout     xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:id="@+id/rl"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:padding="16dp"     tools:context=".MainActivity"     android:background="@android:color/white"     >     <Button         android:id="@+id/btn"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="Align Parent Top"         android:layout_centerInParent="true"         /> </RelativeLayout>
MainActivity.java 
 package com.cfsuman.me.androidcodesnippets;  import android.os.Bundle; import android.app.Activity; import android.view.View; import android.widget.Button; import android.widget.RelativeLayout; import android.widget.RelativeLayout.LayoutParams;  public class MainActivity extends Activity{      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          // Get the widgets reference from XML layout         RelativeLayout rl = (RelativeLayout) findViewById(R.id.rl);         selesai Button btn = (Button) findViewById(R.id.btn);          // Set a click listener for Button widget         btn.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 /*                     LayoutParams are used by views to tell                     their parents how they want to be laid out                      public ViewGroup.LayoutParams getLayoutParams ()                         Get the LayoutParams associated with this view.                         All views should have layout parameters.                         These supply parameters to the parent of this view                         specifying how it should be arranged. There are many                         subclasses of ViewGroup.LayoutParams, and these correspond                         to the different subclasses of ViewGroup that are                         responsible for arranging their children.                  */                 LayoutParams lp = (LayoutParams) btn.getLayoutParams();                 /*                     addRule(int verb)                         Adds a layout rule to be interpreted by the RelativeLayout.                         This method should only be used for constraints that don't                         refer to another sibling (e.g., CENTER_IN_PARENT) or take                         a boolean value (TRUE for true or 0 for false).                      addRule(int verb, int anchor)                         Adds a layout rule to be interpreted by the RelativeLayout.                         Use this for verbs that take a target, such as a sibling                         (ALIGN_RIGHT) or a boolean value (VISIBLE).                      ALIGN_PARENT_TOP                         Rule that aligns the child's top                         edge with its RelativeLayout parent's top edge.                 */                 lp.addRule(RelativeLayout.ALIGN_PARENT_TOP);                  /*                 public void setLayoutParams (ViewGroup.LayoutParams params)                     Set the layout parameters associated with this view.                     These supply parameters to the parent of this view specifying                     how it should be arranged. There are many subclasses of                     ViewGroup.LayoutParams, and these correspond to the different                     subclasses of ViewGroup that are responsible                     for arranging their children.                  */                 btn.setLayoutParams(lp);            }         });     } }
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