计算器

界面代码：

activity_main界面： 

<LinearLayout 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"
    android:orientation="vertical" >
 
    <EditText
        android:id="@+id/et_edit"
        android:layout_width="match_parent"
        android:layout_height="80sp"
        android:focusable="false"
        android:gravity="right"
        android:inputType="text"
        android:singleLine="true"
        android:textSize="40sp" />
 
    <TableLayout
        android:id="@+id/tl_all"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginTop="10sp"
        android:collapseColumns="4" >
 
        <TableRow
            android:id="@+id/tr_one"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent" >
 
            <Button
                android:id="@+id/bt_seven"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="7" />
 
            <Button
                android:id="@+id/bt_eight"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="8" />
 
            <Button
                android:id="@+id/bt_nine"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="9" />
 
            <Button
                android:id="@+id/bt_back"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="back" />
        </TableRow>
 
        <TableRow
            android:id="@+id/tr_two"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent" >
 
            <Button
                android:id="@+id/bt_four"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="4" />
 
            <Button
                android:id="@+id/bt_five"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="5" />
 
            <Button
                android:id="@+id/bt_six"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="6" />
 
            <Button
                android:id="@+id/bt_divide"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="/" />
        </TableRow>
 
        <TableRow
            android:id="@+id/tr_three"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent" >
 
            <Button
                android:id="@+id/bt_one"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="1" />
 
            <Button
                android:id="@+id/bt_two"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="2" />
 
            <Button
                android:id="@+id/bt_three"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="3" />
 
            <Button
                android:id="@+id/bt_multiply"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="*" />
        </TableRow>
 
 
        <TableRow
            android:id="@+id/tr_four"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent" >
 
            <Button
                android:id="@+id/bt_zero"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="0" />
 
            <Button
                android:id="@+id/bt_point"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="." />
 
            <Button
                android:id="@+id/bt_add"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="+" />
 
            <Button
                android:id="@+id/bt_sub"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="-" />
        </TableRow>
 
        <TableRow
            android:id="@+id/tr_five"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent" >
 
            <Button
                android:id="@+id/bt_equal"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:layout_weight="3"
                android:text="=" />
 
            <Button
                android:id="@+id/bt_clear"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:text="clear" />
        </TableRow>
    </TableLayout>
 
</LinearLayout>

mainactivity界面：

package com.example.jsq;

import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
 
public class MainActivity extends Activity {
 
    private Button bt_zero;
    private Button bt_one;
    private Button bt_two;
    private Button bt_three;
    private Button bt_four;
    private Button bt_five;
    private Button bt_six;
    private Button bt_seven;
    private Button bt_eight;
    private Button bt_nine;
    private Button bt_back;
    private Button bt_multiply;
    private Button bt_divide;
    private Button bt_sub;
    private Button bt_add;
    private Button bt_point;
    private Button bt_equal;
    private Button bt_clear;
    private EditText et_edit;
 
    private StringBuffer str_display = new StringBuffer();
    private boolean flag = true;
    private String str_oper = "+";
    private String str_result = "0";
    private double num1;
    private double num2;
    private boolean b_sub;
    private boolean b_mul;
    private boolean b_div;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        bt_zero = (Button) findViewById(R.id.bt_zero);
        bt_one = (Button) findViewById(R.id.bt_one);
        bt_two = (Button) findViewById(R.id.bt_two);
        bt_three = (Button) findViewById(R.id.bt_three);
        bt_four = (Button) findViewById(R.id.bt_four);
        bt_five = (Button) findViewById(R.id.bt_five);
        bt_six = (Button) findViewById(R.id.bt_six);
        bt_seven = (Button) findViewById(R.id.bt_seven);
        bt_eight = (Button) findViewById(R.id.bt_eight);
        bt_nine = (Button) findViewById(R.id.bt_nine);
        bt_back = (Button) findViewById(R.id.bt_back);
        bt_multiply = (Button) findViewById(R.id.bt_multiply);
        bt_divide = (Button) findViewById(R.id.bt_divide);
        bt_sub = (Button) findViewById(R.id.bt_sub);
        bt_add = (Button) findViewById(R.id.bt_add);
        bt_point = (Button) findViewById(R.id.bt_point);
        bt_equal = (Button) findViewById(R.id.bt_equal);
        bt_clear = (Button) findViewById(R.id.bt_clear);
        et_edit = (EditText) findViewById(R.id.et_edit);
        et_edit.setText("0.0");
 
        bt_zero.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("0");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_one.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("1");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_two.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("2");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_three.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("3");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_four.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("4");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_five.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("5");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_six.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("6");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_seven.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("7");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_eight.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("8");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_nine.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_display.append("9");
                et_edit.setText(str_display.toString());
            }
        });
 
        bt_point.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                if (flag) {
                    str_display.append(".");
                    et_edit.setText(str_display.toString());
                    flag = false;
                }
            }
        });
 
        bt_back.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                if (str_display.length() != 0) {
                    str_display.deleteCharAt(str_display.length() - 1);
                    et_edit.setText(str_display.toString());
                }
            }
        });
 
        bt_add.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_oper = "+";
                if (str_display.toString() != "") {
                    num1 += Double.parseDouble(str_display.toString());
                    str_display = new StringBuffer("");
                }
                // 在按了“=”而没有输入数字时，str_result不为空；在按了“=”并且输入数字后，str_result结果为空。（后面同理）
                if (str_result != null) {
                    num1 = Double.parseDouble(str_result);
                    str_result = null;
                }
                et_edit.setText(String.valueOf(num1));
                flag = true;
            }
        });
 
        bt_sub.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_oper = "-";
                if (b_sub == false && str_display.toString() != "") {
                    num1 = Double.parseDouble(str_display.toString());
                    et_edit.setText(String.valueOf(num1));
                    str_display = new StringBuffer("");
                    b_sub = true;
                } else {
                    if (str_display.toString() != "") {
                        num1 -= Double.parseDouble(str_display.toString());
                        str_display = new StringBuffer("");
                    }
                    if (str_result != null) {
                        num1 = Double.parseDouble(str_result);
                        str_result = null;
                    }
                    et_edit.setText(String.valueOf(num1));
                }
                flag = true;
            }
        });
 
        bt_divide.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_oper = "/";
                if (b_div == false && str_display.toString() != null) {
                    num1 = Double.parseDouble(str_display.toString());
                    et_edit.setText(String.valueOf(num1));
                    str_display = new StringBuffer("");
                    b_div = true;
                } else {
                    if (str_display.toString() != "") {
                        if (Double.parseDouble(str_display.toString()) == 0) {
                            Toast.makeText(MainActivity.this, "除数不能为零！", 0)
                                    .show();
                        } else {
                            num1 /= Double.parseDouble(str_display.toString());
                            str_display = new StringBuffer("");
                        }
                    }
                    if (str_result != null) {
                        num1 = Double.parseDouble(str_result);
                        str_result = null;
                    }
                    et_edit.setText(String.valueOf(num1));
                }
                flag = true;
            }
        });
 
        bt_multiply.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_oper = "*";
                if (b_mul == false && str_display.toString() != "") {
                    num1 = Double.parseDouble(str_display.toString());
                    et_edit.setText(String.valueOf(num1));
                    str_display = new StringBuffer("");
                    b_mul = true;
                } else {
                    if (str_display.toString() != "") {
                        num1 *= Double.parseDouble(str_display.toString());
                        str_display = new StringBuffer("");
                    }
                    if (str_result != null) {
                        num1 = Double.parseDouble(str_result);
                        str_result = null;
                    }
                    et_edit.setText(String.valueOf(num1));
                }
                flag = true;
            }
        });
 
        bt_equal.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                if (str_oper.equals("+")) {
                    num2 = Double.parseDouble(str_display.toString());
                    str_result = String.valueOf(num1 + num2);
                    et_edit.setText(str_result);
                    str_display = new StringBuffer("");
                }
                if (str_oper.equals("-")) {
                    num2 = Double.parseDouble(str_display.toString());
                    str_result = String.valueOf(num1 - num2);
                    et_edit.setText(str_result);
                    str_display = new StringBuffer("");
                }
                if (str_oper.equals("*")) {
                    num2 = Double.parseDouble(str_display.toString());
                    str_result = String.valueOf(num1 * num2);
                    et_edit.setText(str_result);
                    str_display = new StringBuffer("");
                }
                if (str_oper.equals("/")) {
                    num2 = Double.parseDouble(str_display.toString());
                    if (num2 != 0) {
                        str_result = String.valueOf(num1 / num2);
                        et_edit.setText(str_result);
                    } else {
                        Toast.makeText(MainActivity.this, "除数不能为零！", 0).show();
                    }
                    str_display = new StringBuffer("");
                }
            }
        });
 
        bt_clear.setOnClickListener(new OnClickListener() {
 
            public void onClick(View v) {
                str_oper = "+";
                str_display = new StringBuffer("");
                str_result = null;
                num1 = 0;
                num2 = 0;
                flag = true;
                b_div = false;
                b_mul = false;
                b_sub = false;
                et_edit.setText("0.0");
            }
        });
    }
 
}

运行截屏：