AndroidStudio实现简单计算器功能

public class MainActivity extends AppCompatActivity {
 
 private TextView txt; /*显示计算过程及结果*/
 private Button butp,but1,but2,but3,but4,but5,but6,but7,but8,but9,but0,buta,buts,butm,butdiv,butdopt,buteq;
 double num1=0,num2=0;
 double result=0; /*计算结果*/
 int op=0; /*判断操作数*/
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 txt=(TextView) findViewById(R.id.textView); /*与用户界面程序中组件建立关联*/
 butp=(Button)findViewById(R.id.butCancel); /*清除*/
 but1=(Button)findViewById(R.id.but_1); 
 but2=(Button)findViewById(R.id.but_2);
 but3=(Button)findViewById(R.id.but_3);
 but4=(Button)findViewById(R.id.but_4);
 but5=(Button)findViewById(R.id.but_5);
 but6=(Button)findViewById(R.id.but_6);
 but7=(Button)findViewById(R.id.but_7);
 but8=(Button)findViewById(R.id.but_8);
 but9=(Button)findViewById(R.id.but_9);
 but0=(Button)findViewById(R.id.but_0);
 buta=(Button)findViewById(R.id.but_add); /*加*/
 buts=(Button)findViewById(R.id.but_sub); /*减*/
 butm=(Button)findViewById(R.id.but_mut); /*乘*/
 butdiv=(Button)findViewById(R.id.but_div); /*除*/
 butdopt=(Button)findViewById(R.id.but_dopt); /*点*/
 buteq=(Button)findViewById(R.id.but_equ); /*等于*/
 
 
 butp.setOnClickListener(new mClick());
 but1.setOnClickListener(new mClick());
 but2.setOnClickListener(new mClick());
 but3.setOnClickListener(new mClick());
 but4.setOnClickListener(new mClick());
 but5.setOnClickListener(new mClick());
 but6.setOnClickListener(new mClick());
 but7.setOnClickListener(new mClick());
 but8.setOnClickListener(new mClick());
 but9.setOnClickListener(new mClick());
 but0.setOnClickListener(new mClick());
 buta.setOnClickListener(new mClick());
 buts.setOnClickListener(new mClick());
 butm.setOnClickListener(new mClick());
 butdiv.setOnClickListener(new mClick());
 butdopt.setOnClickListener(new mClick());
 buteq.setOnClickListener(new mClick());
 }

class mClick implements View.OnClickListener
 {
 public void onClick(View v) {
 
 switch(v.getId()){ /*用swtich（）方法，判断点击按钮的id*/
 case R.id.butCancel: /*清除，直接将输入的所有符号清空*/
 txt.setText(null);
 break;
 /*数字，小数点按键*/
 case R.id.but_1:
 String str1=txt.getText().toString(); /*获取输入内容并转为string类型/
 str1+="1"; /*拼接字符串*/
 txt.setText(str1); /*显示输入内容*/
 break;
 case R.id.but_2:
 String str2=txt.getText().toString();
 str2+="2";
 txt.setText(str2);
 break;
 case R.id.but_3:
 String str3=txt.getText().toString();
 str3+="3";
 txt.setText(str3);
 break;
 case R.id.but_4:
 String str4=txt.getText().toString();
 str4+="4";
 txt.setText(str4);
 break;
 case R.id.but_5:
 String str5=txt.getText().toString();
 str5+="5";
 txt.setText(str5);
 break;
 case R.id.but_6:
 String str6=txt.getText().toString();
 str6+="6";
 txt.setText(str6);
 break;
 case R.id.but_7:
 String str7=txt.getText().toString();
 str7+="7";
 txt.setText(str7);
 break;
 case R.id.but_8:
 String str8=txt.getText().toString();
 str8+="8";
 txt.setText(str8);
 break;
 case R.id.but_9:
 String str9=txt.getText().toString();
 str9+="9";
 txt.setText(str9);
 break;
 case R.id.but_0:
 String strr=txt.getText().toString();
 strr+="0";
 txt.setText(strr);
 break;
 case R.id.but_dopt:
 String strd=txt.getText().toString();
 strd+=".";
 txt.setText(strd);
 break;

/*运算符按键*/
 case R.id.but_add:
 String stradd=txt.getText().toString();/*按运算符，获取要计算的数字，并放入num1等待计算*/
 if(stradd.equals(null)) /*判断按运算符前是否输入要计算的数字，若为空，则返回*/
 {
 return;
 }
 num1=Double.valueOf(stradd);/*将获取的字符串转化为double类型以便计算*/
 txt.setText(null);
 op=1;
 break;
 case R.id.but_sub:
 String strsub=txt.getText().toString();
 if(strsub.equals(null))
 {
 return;
 }
 num1=Double.valueOf(strsub);
 txt.setText(null);
 op=2;
 break;
 case R.id.but_mut:
 String strmut=txt.getText().toString();
 if(strmut.equals(null))
 {
 return;
 }
 num1=Double.valueOf(strmut);
 txt.setText(null);
 op=3;
 break;
 case R.id.but_div:
 String strdiv=txt.getText().toString();
 if(strdiv.equals(null))
 {
 return;
 }
 num1=Double.valueOf(strdiv);
 txt.setText(null);
 op=4;
 break;

case R.id.but_equ:
 String strequ=txt.getText().toString();
 num2=Double.valueOf(strequ);
 txt.setText(null);
 switch (op){ /*用switch函数来判断进行何种操作，实施运算并得出结果*/
 case 1:
 result=num1+num2;
 txt.setText(String.valueOf(num1)+"+"+String.valueOf(num2)+"="+String.valueOf(result));/*获取结果并将其转为字符串输出*/
 break;
 case 2:
 result=num1-num2;
 txt.setText(String.valueOf(num1)+"-"+String.valueOf(num2)+"="+String.valueOf(result));
 break;
 case 3:
 result=num1*num2;
 txt.setText(String.valueOf(num1)+"*"+String.valueOf(num2)+"="+String.valueOf(result));
 break;
 case 4:
 if (num2==0){
 txt. setText("除数不能为0！"); /*规定除数不能为0，否则报错*/
 }else{
 result=num1/num2;
 txt.setText(String.valueOf(num1)+"/"+String.valueOf(num2)+"="+String.valueOf(result));}
 break;
 default:
 result=0;
 break;
 }