用最简洁的代码写出一个计算器android studio代码

以下是一个简单的计算器应用程序的 Android Studio 代码：

MainActivity.java

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

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    Button btn0, btn1, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9, btnAdd, btnSubtract, btnMultiply, btnDivide, btnEquals, btnDecimal, btnClear;
    TextView display;
    String currentNumber;
    String operation;
    double result;

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

        btn0 = findViewById(R.id.btn0);
        btn1 = findViewById(R.id.btn1);
        btn2 = findViewById(R.id.btn2);
        btn3 = findViewById(R.id.btn3);
        btn4 = findViewById(R.id.btn4);
        btn5 = findViewById(R.id.btn5);
        btn6 = findViewById(R.id.btn6);
        btn7 = findViewById(R.id.btn7);
        btn8 = findViewById(R.id.btn8);
        btn9 = findViewById(R.id.btn9);
        btnAdd = findViewById(R.id.btnAdd);
        btnSubtract = findViewById(R.id.btnSubtract);
        btnMultiply = findViewById(R.id.btnMultiply);
        btnDivide = findViewById(R.id.btnDivide);
        btnEquals = findViewById(R.id.btnEquals);
        btnDecimal = findViewById(R.id.btnDecimal);
        btnClear = findViewById(R.id.btnClear);

        display = findViewById(R.id.display);

        btn0.setOnClickListener(this);
        btn1.setOnClickListener(this);
        btn2.setOnClickListener(this);
        btn3.setOnClickListener(this);
        btn4.setOnClickListener(this);
        btn5.setOnClickListener(this);
        btn6.setOnClickListener(this);
        btn7.setOnClickListener(this);
        btn8.setOnClickListener(this);
        btn9.setOnClickListener(this);
        btnAdd.setOnClickListener(this);
        btnSubtract.setOnClickListener(this);
        btnMultiply.setOnClickListener(this);
        btnDivide.setOnClickListener(this);
        btnEquals.setOnClickListener(this);
        btnDecimal.setOnClickListener(this);
        btnClear.setOnClickListener(this);

        currentNumber = "";
        operation = "";
        result = 0;
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btn0:
                currentNumber += "0";
                display.setText(currentNumber);
                break;
            case R.id.btn1:
                currentNumber += "1";
                display.setText(currentNumber);
                break;
            case R.id.btn2:
                currentNumber += "2";
                display.setText(currentNumber);
                break;
            case R.id.btn3:
                currentNumber += "3";
                display.setText(currentNumber);
                break;
            case R.id.btn4:
                currentNumber += "4";
                display.setText(currentNumber);
                break;
            case R.id.btn5:
                currentNumber += "5";
                display.setText(currentNumber);
                break;
            case R.id.btn6:
                currentNumber += "6";
                display.setText(currentNumber);
                break;
            case R.id.btn7:
                currentNumber += "7";
                display.setText(currentNumber);
                break;
            case R.id.btn8:
                currentNumber += "8";
                display.setText(currentNumber);
                break;
            case R.id.btn9:
                currentNumber += "9";
                display.setText(currentNumber);
                break;
            case R.id.btnAdd:
                calculate();
                operation = "+";
                break;
            case R.id.btnSubtract:
                calculate();
                operation = "-";
                break;
            case R.id.btnMultiply:
                calculate();
                operation = "*";
                break;
            case R.id.btnDivide:
                calculate();
                operation = "/";
                break;
            case R.id.btnEquals:
                calculate();
                operation = "";
                break;
            case R.id.btnDecimal:
                if (!currentNumber.contains(".")) {
                    currentNumber += ".";
                }
                display.setText(currentNumber);
                break;
            case R.id.btnClear:
                currentNumber = "";
                operation = "";
                result = 0;
                display.setText("");
                break;
        }
    }

    private void calculate() {
        if (currentNumber.length() > 0) {
            double number = Double.parseDouble(currentNumber);
            currentNumber = "";
            if (operation.equals("+")) {
                result += number;
            } else if (operation.equals("-")) {
                result -= number;
            } else if (operation.equals("*")) {
                result *= number;
            } else if (operation.equals("/")) {
                result /= number;
            } else {
                result = number;
            }
            display.setText("" + result);
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/display"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:gravity="right"
        android:padding="16dp"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <Button
        android:id="@+id/btnClear"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/display"
        android:layout_toLeftOf="@+id/btnDivide"
        android:layout_weight="1"
        android:text="C" />

    <Button
        android:id="@+id/btnDivide"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/display"
        android:layout_toLeftOf="@+id/btnMultiply"
        android:layout_weight="1"
        android:text="/" />

    <Button
        android:id="@+id/btnMultiply"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/display"
        android:layout_toLeftOf="@+id/btnSubtract"
        android:layout_weight="1"
        android:text="*" />

    <Button
        android:id="@+id/btnSubtract"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/display"
        android:layout_toLeftOf="@+id/btnAdd"
        android:layout_weight="1"
        android:text="-" />

    <Button
        android:id="@+id/btnAdd"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/display"
        android:layout_toLeftOf="@+id/btnEquals"
        android:layout_weight="1"
        android:text="+" />

    <Button
        android:id="@+id/btnEquals"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/display"
        android:layout_alignParentRight="true"
        android:layout_weight="1"
        android:text="=" />

    <Button
        android:id="@+id/btn7"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btnClear"
        android:layout_toLeftOf="@+id/btn8"
        android:layout_weight="1"
        android:text="7" />

    <Button
        android:id="@+id/btn8"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btnClear"
        android:layout_toLeftOf="@+id/btn9"
        android:layout_weight="1"
        android:text="8" />

    <Button
        android:id="@+id/btn9"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btnClear"
        android:layout_toLeftOf="@+id/btnDivide"
        android:layout_weight="1"
        android:text="9" />

    <Button
        android:id="@+id/btn4"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn7"
        android:layout_toLeftOf="@+id/btn5"
        android:layout_weight="1"
        android:text="4" />

    <Button
        android:id="@+id/btn5"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn8"
        android:layout_toLeftOf="@+id/btn6"
        android:layout_weight="1"
        android:text="5" />

    <Button
        android:id="@+id/btn6"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn9"
        android:layout_toLeftOf="@+id/btnMultiply"
        android:layout_weight="1"
        android:text="6" />

    <Button
        android:id="@+id/btn1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn4"
        android:layout_toLeftOf="@+id/btn2"
        android:layout_weight="1"
        android:text="1" />

    <Button
        android:id="@+id/btn2"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn5"
        android:layout_toLeftOf="@+id/btn3"
        android:layout_weight="1"
        android:text="2" />

    <Button
        android:id="@+id/btn3"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn6"
        android:layout_toLeftOf="@+id/btnSubtract"
        android:layout_weight="1"
        android:text="3" />

    <Button
        android:id="@+id/btnDecimal"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn0"
        android:layout_toLeftOf="@+id/btnEquals"
        android:layout_weight="1"
        android:text="." />

    <Button
        android:id="@+id/btn0"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/btnClear"
        android:layout_toLeftOf="@+id/btnDecimal"
        android:layout_weight="1"
        android:text="0" />

</RelativeLayout>