demo

package com.app.cceasy.macconvert;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    public void getResult(View view){

        EditText edit_text1 = (EditText) findViewById(R.id.edit_text1);
        EditText edit_text2 = (EditText) findViewById(R.id.edit_text2);
        EditText edit_text3 = (EditText) findViewById(R.id.edit_text3);
        TextView result = (TextView) findViewById(R.id.textview);
        Long macStart = Long.parseLong(edit_text1.getText().toString(),16);
        Long num1 = Long.parseLong(edit_text2.getText().toString(),10);
        Long num2 = Long.parseLong(edit_text3.getText().toString(),10);

        result.setTextSize(30);
        result.setText(macStart.toHexString(macStart+num1*num2-1));
        //result.setText(edit_text1.getText().toString()+edit_text2.getText().toString()+edit_text3.getText().toString());
    }
    public void clearData(View view){
        EditText edit_text1 = (EditText) findViewById(R.id.edit_text1);
        EditText edit_text2 = (EditText) findViewById(R.id.edit_text2);
        EditText edit_text3 = (EditText) findViewById(R.id.edit_text3);
        TextView result = (TextView) findViewById(R.id.textview);
        edit_text1.setText("");
        edit_text2.setText("");
        edit_text3.setText("");
        result.setText("");
        //(EditText) findViewById(R.id.edit_text2).setText("");
        //(EditText) findViewById(R.id.edit_text3).setText("");
       // (TextView) findViewById(R.id.textview).setText("");
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.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();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <EditText
            android:id="@+id/edit_text1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="macstart" />
        <EditText
            android:id="@+id/edit_text2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:hint="num1" />
        <EditText
            android:id="@+id/edit_text3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:hint="num2" />
        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="计算"
            android:onClick="getResult" />

    </LinearLayout >

    <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:orientation="horizontal" >
        <TextView
            android:id="@+id/textview"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="result" />
    </LinearLayout >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:gravity="bottom|right">
        <Button
            android:id="@+id/cleardata"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="clearData"
            android:hint="清除" />
    </LinearLayout >

</LinearLayout >