روند کردن اعداد اعشاری

سلام چجوری میشه عددی رو که توی خروجی 18.92351231 هست رو به 18.92 روند کرد؟

یه کد توی اینترنت پیدا کردم به این شکل:

 double roundTwoDecimals(double d)
{
    DecimalFormat twoDForm = new DecimalFormat("#.##");
    return Double.valueOf(twoDForm.format(d));
}

فقط نمیدونم کجا استفادش کنم :|

کد برنامه ام اینه:

 package com.yekteam.bmicalculator;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.os.Build;

public class MainActivity extends ActionBarActivity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  final EditText numWeight = (EditText) findViewById(R.id.numWeight);
  final EditText numHeight = (EditText) findViewById(R.id.numHeight);
  final Button btnCalculate = (Button) findViewById(R.id.btnCalculate);
  final TextView txtResult = (TextView) findViewById(R.id.txtResult);
  
  
  btnCalculate.setOnClickListener(new OnClickListener() {
   
   @Override
   public void onClick(View arg0) {
    String Weight = numWeight.getText().toString();
    double i = Double.parseDouble(Weight);
    String Height = numHeight.getText().toString();
    double j = Double.parseDouble(Height);
    double k;
    k = i/(j*j);
    txtResult.setText("Your BMI is: " + k);

   }
  });
  if (savedInstanceState == null) {
  }
 }

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {

  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater().inflate(R.menu.main, menu);
  return true;
 }

 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
  // Handle action bar item clicks here. The action bar will
  // automatically handle clicks on the Home/Up button, so long
  // as you specify a parent activity in AndroidManifest.xml.
  int id = item.getItemId();
  if (id == R.id.action_settings) {
   return true;
  }
  return super.onOptionsItemSelected(item);
 }


 }