用android studio 写一个计算器代码

好的，以下是一个简单的计算器代码：

public class MainActivity extends AppCompatActivity {

    private EditText etInput;
    private TextView tvOutput;

    private double num1 = 0, num2 = 0;
    private String operator = "";

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

        etInput = findViewById(R.id.et_input);
        tvOutput = findViewById(R.id.tv_output);

        Button btn0 = findViewById(R.id.btn_0);
        Button btn1 = findViewById(R.id.btn_1);
        Button btn2 = findViewById(R.id.btn_2);
        Button btn3 = findViewById(R.id.btn_3);
        Button btn4 = findViewById(R.id.btn_4);
        Button btn5 = findViewById(R.id.btn_5);
        Button btn6 = findViewById(R.id.btn_6);
        Button btn7 = findViewById(R.id.btn_7);
        Button btn8 = findViewById(R.id.btn_8);
        Button btn9 = findViewById(R.id.btn_9);
        Button btnAdd = findViewById(R.id.btn_add);
        Button btnSubtract = findViewById(R.id.btn_subtract);
        Button btnMultiply = findViewById(R.id.btn_multiply);
        Button btnDivide = findViewById(R.id.btn_divide);
        Button btnEquals = findViewById(R.id.btn_equals);
        Button btnClear = findViewById(R.id.btn_clear);

        View.OnClickListener onClickListener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                switch (v.getId()) {
                    case R.id.btn_0:
                        etInput.append("0");
                        break;
                    case R.id.btn_1:
                        etInput.append("1");
                        break;
                    case R.id.btn_2:
                        etInput.append("2");
                        break;
                    case R.id.btn_3:
                        etInput.append("3");
                        break;
                    case R.id.btn_4:
                        etInput.append("4");
                        break;
                    case R.id.btn_5:
                        etInput.append("5");
                        break;
                    case R.id.btn_6:
                        etInput.append("6");
                        break;
                    case R.id.btn_7:
                        etInput.append("7");
                        break;
                    case R.id.btn_8:
                        etInput.append("8");
                        break;
                    case R.id.btn_9:
                        etInput.append("9");
                        break;
                    case R.id.btn_add:
                        operator = "+";
                        num1 = Double.parseDouble(etInput.getText().toString());
                        etInput.setText("");
                        break;
                    case R.id.btn_subtract:
                        operator = "-";
                        num1 = Double.parseDouble(etInput.getText().toString());
                        etInput.setText("");
                        break;
                    case R.id.btn_multiply:
                        operator = "*";
                        num1 = Double.parseDouble(etInput.getText().toString());
                        etInput.setText("");
                        break;
                    case R.id.btn_divide:
                        operator = "/";
                        num1 = Double.parseDouble(etInput.getText().toString());
                        etInput.setText("");
                        break;
                    case R.id.btn_equals:
                        num2 = Double.parseDouble(etInput.getText().toString());
                        double result = 0;
                        switch (operator) {
                            case "+":
                                result = num1 + num2;
                                break;
                            case "-":
                                result = num1 - num2;
                                break;
                            case "*":
                                result = num1 * num2;
                                break;
                            case "/":
                                result = num1 / num2;
                                break;
                        }
                        tvOutput.setText(String.valueOf(result));
                        break;
                    case R.id.btn_clear:
                        etInput.setText("");
                        tvOutput.setText("");
                        num1 = 0;
                        num2 = 0;
                        break;
                }
            }
        };

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

在 XML 文件中，你需要创建一个包含 EditText 和 TextView 的布局。这里是一个例子：

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <EditText
        android:id="@+id/et_input"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Enter numbers here"
        android:inputType="number"/>

    <TextView
        android:id="@+id/tv_output"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="24sp"
        android:gravity="center"/>

    <GridLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:columnCount="4"
        android:rowCount="5"
        android:padding="16dp">

        <Button
            android:id="@+id/btn_7"
            android:layout_column="0"
            android:layout_row="0"
            android:text="7"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_8"
            android:layout_column="1"
            android:layout_row="0"
            android:text="8"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_9"
            android:layout_column="2"
            android:layout_row="0"
            android:text="9"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_divide"
            android:layout_column="3"
            android:layout_row="0"
            android:text="/"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_4"
            android:layout_column="0"
            android:layout_row="1"
            android:text="4"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_5"
            android:layout_column="1"
            android:layout_row="1"
            android:text="5"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_6"
            android:layout_column="2"
            android:layout_row="1"
            android:text="6"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_multiply"
            android:layout_column="3"
            android:layout_row="1"
            android:text="*"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_1"
            android:layout_column="0"
            android:layout_row="2"
            android:text="1"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_2"
            android:layout_column="1"
            android:layout_row="2"
            android:text="2"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_3"
            android:layout_column="2"
            android:layout_row="2"
            android:text="3"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_subtract"
            android:layout_column="3"
            android:layout_row="2"
            android:text="-"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_0"
            android:layout_column="0"
            android:layout_row="3"
            android:layout_columnSpan="2"
            android:text="0"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_clear"
            android:layout_column="2"
            android:layout_row="3"
            android:text="C"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_add"
            android:layout_column="3"
            android:layout_row="3"
            android:text="+"
            android:textSize="20sp"/>

        <Button
            android:id="@+id/btn_equals"
            android:layout_column="0"
            android:layout_row="4"
            android:layout_columnSpan="4"
            android:text="="
            android:textSize="20sp"/>

    </GridLayout>

</LinearLayout>

这个代码仅仅是一个简单的例子，你可以根据自己的需要进行修改和扩展。