Android Studio如何实现长方体表面积计算器

package com.example.flyyu.four;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

import java.util.regex.Pattern;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 }
 @Override
 public void onClick(View v) {
 EditText a=(EditText)findViewById(R.id.editText);

 EditText b=(EditText)findViewById(R.id.editText2);

 EditText c=(EditText)findViewById(R.id.editText3);
 Intent it=new Intent(this,biapmianji.class);
 if (!isNumber(a.getText().toString())&&!isNumber(b.getText().toString())&&!isNumber(c.getText().toString())){
 it.putExtra("a",a.getText().toString());
 it.putExtra("b",b.getText().toString());
 it.putExtra("c",c.getText().toString());
 MainActivity.this.startActivity(it);
 }
 }
 public boolean isNumber(String s){

 String pattern = ".*\\D.*";

 boolean isMatch = Pattern.matches(pattern,s);
 if (isMatch||s.length()==0){
 Toast.makeText(this,"输入异常",Toast.LENGTH_SHORT).show();
 return true;
 }
 return isMatch;
 }
}

package com.example.flyyu.four;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class biapmianji extends AppCompatActivity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_biapmianji);
 TextView textView=(TextView)findViewById(R.id.textView4);
 Intent it=this.getIntent();
 float a=Float.valueOf(it.getStringExtra("a")) ;
 float b=Float.valueOf(it.getStringExtra("b")) ;
 float c=Float.valueOf(it.getStringExtra("c")) ;
 String s=(2*(a*b+a*c+b*c))+"";
 textView.setText("该长方体的表面积为:"+s);

// textView.setText("该长方体的表面积为:"+a);
 }


}

<&#63;xml version="1.0" encoding="utf-8"&#63;>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:app="http://schemas.android.com/apk/res-auto"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context="com.example.flyyu.four.biapmianji">

 <TextView
 android:id="@+id/textView4"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_marginBottom="8dp"
 android:layout_marginLeft="8dp"
 android:layout_marginRight="8dp"
 android:layout_marginTop="8dp"
 android:text="TextView"
 android:textSize="18sp"
 app:layout_constraintBottom_toBottomOf="parent"
 app:layout_constraintHorizontal_bias="0.174"
 app:layout_constraintLeft_toLeftOf="parent"
 app:layout_constraintRight_toRightOf="parent"
 app:layout_constraintTop_toTopOf="parent"
 app:layout_constraintVertical_bias="0.083" />
</android.support.constraint.ConstraintLayout>

<&#63;xml version="1.0" encoding="utf-8"&#63;>
<!--<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"-->

<android.widget.LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:app="http://schemas.android.com/apk/res-auto"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical"
 tools:context="com.example.flyyu.four.MainActivity">

 <TextView
 android:id="@+id/textView"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:text="长：" />

 <EditText
 android:id="@+id/editText"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:ems="10"
 android:inputType="text" />

 <TextView
 android:id="@+id/textView2"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:text="宽：" />

 <EditText
 android:id="@+id/editText2"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:ems="10"
 android:inputType="text" />

 <TextView
 android:id="@+id/textView3"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:text="高：" />

 <EditText
 android:id="@+id/editText3"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:ems="10"
 android:inputType="text" />

 <Button
 android:id="@+id/button"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:onClick="onClick"
 android:text="计算" />
</android.widget.LinearLayout>