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   源码介绍

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Android studio实现简易计算器功能（UI界面模仿的小米计算器），能够实现加减乘除取余运算以及退格和清屏功能，并且可以在旋转屏幕时能够保存竖屏时的数据，在横屏切换为竖屏时也能实现数据回传

package com.example.datepickdemo;

import androidx.appcompat.app.AppCompatActivity;

import android.content.pm.ActivityInfo;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.FrameLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;

import java.util.Arrays;
import java.util.Calendar;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private Button btn_0,btn_1,btn_2,btn_3,btn_4,btn_5,btn_6,btn_7,btn_8,btn_9;
    private Button btn_point; //小数点
    private Button btn_clear; //清除
    private Button btn_del;   //删除
    private Button btn_plus;
    private Button btn_percent;
    private Button btn_minus;
    private Button btn_multiply;
    private Button btn_divide;
    private Button btn_equal;
    private TextView et_input;
    private TextView et_res;

    private StringBuilder pending = new StringBuilder();

    private void initView() {
        et_input = (TextView) findViewById(R.id.calculator_screen);
        et_res = (TextView) findViewById(R.id.res);
        btn_0 = (Button) findViewById(R.id.button_0);
        btn_1 = (Button) findViewById(R.id.button_1);
        btn_2 = (Button) findViewById(R.id.button_2);
        btn_3 = (Button) findViewById(R.id.button_3);
        btn_4 = (Button) findViewById(R.id.button_4);
        btn_5 = (Button) findViewById(R.id.button_5);
        btn_6 = (Button) findViewById(R.id.button_6);
        btn_7 = (Button) findViewById(R.id.button_7);
        btn_8 = (Button) findViewById(R.id.button_8);
        btn_9 = (Button) findViewById(R.id.button_9);
        btn_point = (Button) findViewById(R.id.button_dot);
        btn_clear = (Button) findViewById(R.id.button_clear);
        btn_del = (Button) findViewById(R.id.button_del);
        btn_plus = (Button) findViewById(R.id.button_add);
        btn_minus = (Button) findViewById(R.id.button_minus);
        btn_multiply = (Button) findViewById(R.id.button_multiply);
        btn_divide = (Button) findViewById(R.id.button_divide);
        btn_equal = (Button) findViewById(R.id.button_equal);
        btn_percent = (Button) findViewById(R.id.button_percent);

        btn_0.setOnClickListener(this);
        btn_1.setOnClickListener(this);
        btn_2.setOnClickListener(this);
        btn_3.setOnClickListener(this);
        btn_4.setOnClickListener(this);
        btn_5.setOnClickListener(this);
        btn_6.setOnClickListener(this);
        btn_7.setOnClickListener(this);
        btn_8.setOnClickListener(this);
        btn_9.setOnClickListener(this);
        btn_point.setOnClickListener(this);
        btn_plus.setOnClickListener(this);
        btn_equal.setOnClickListener(this);
        btn_minus.setOnClickListener(this);
        btn_multiply.setOnClickListener(this);
        btn_del.setOnClickListener(this);
        btn_divide.setOnClickListener(this);
        btn_clear.setOnClickListener(this);
        btn_divide.setOnClickListener(this);
        btn_percent.setOnClickListener(this);
    }

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

    }

    @Override
    public void onSaveInstanceState(Bundle outstate){
        String num1 = (String) et_input.getText();
        String num2 = (String) et_res.getText();
        super.onSaveInstanceState(outstate);
        outstate.putString("key1",num1);
        outstate.putString("key2",num2);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState){
        super.onRestoreInstanceState(savedInstanceState);
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_FULL_SENSOR);
        setContentView(R.layout.activity_main);
        initView();
        if(savedInstanceState != null){
            String position1 = savedInstanceState.getString("key1");
            String position2 = savedInstanceState.getString("key2");
            et_input.setText(position1);
            et_res.setText(position2);
        }
    }



    public void onClick (View v) {
        int last = 0;
        if(pending.length()!=0)
        {
            last = pending.codePointAt(pending.length()-1);

        }
        switch (v.getId()) {
            case R.id.button_0:
                pending = pending.append("0");
                et_input.setText(pending);
                break;
            case R.id.button_1:
                pending = pending.append("1");
                et_input.setText(pending);
                break;
            case R.id.button_2:
                pending = pending.append("2");
                et_input.setText(pending);
                break;
            case R.id.button_3:
                pending = pending.append("3");
                et_input.setText(pending);
                break;
            case R.id.button_4:
                pending = pending.append("4");
                et_input.setText(pending);
                break;
            case R.id.button_5:
                pending = pending.append("5");
                et_input.setText(pending);
                break;
            case R.id.button_6:
                pending = pending.append("6");
                et_input.setText(pending);
                break;
            case R.id.button_7:
                pending = pending.append("7");
                et_input.setText(pending);
                break;
            case R.id.button_8:
                pending = pending.append("8");
                et_input.setText(pending);
                break;
            case R.id.button_9:
                pending = pending.append("9");
                et_input.setText(pending);
                break;
            case R.id.button_add:
                pending = pending.append(" ");
                et_input.setText(pending);
                break;
            case R.id.button_minus:
                pending = pending.append("-");
                et_input.setText(pending);
                break;
            case R.id.button_multiply:
                pending = pending.append("×");
                et_input.setText(pending);
                break;
            case R.id.button_divide:
                pending = pending.append("÷");
                et_input.setText(pending);
                break;
            case R.id.button_dot:
                if (judje1()) {
                    pending = pending.append(".");
                    et_input.setText(pending);
                }
                break;

            case R.id.button_percent:
                if (judje1()) {
                    pending = pending.append("%");
                    et_input.setText(pending);
                }
                break;

            case R.id.button_del: //删除
                if (pending.length() != 0) {
                    pending = pending.delete(pending.length() - 1, pending.length());
                    et_input.setText(pending);
                }
                break;
            case R.id.button_clear: //清空
                pending = pending.delete(0, pending.length());
                et_input.setText(pending);
                et_res.setText("0");
                break;
            case R.id.button_equal: //等于
                if ((pending.length() > 1)) {
                    InfixInToDuffix inf = new InfixInToDuffix();
                    String res;
                    try {
                        String a = inf.toSuffix(pending);
                        res = inf.dealEquation(a);

                    } catch (Exception ex) {
                        res = "Error";
                    }
                    et_res.setText(res);
                    pending = pending.delete(0, pending.length());
                    if (Character.isDigit(res.charAt(0))) {
                        pending = pending.append(res);
                    }
                }
                break;
            default:
                break;
        }
    }

    private boolean judje1() {
        String a = " -×÷.";
        int[] b = new int[a.length()];
        int max;
        for (int i = 0; i < a.length(); i  ) {
            String c = ""   a.charAt(i);
            b[i] = pending.lastIndexOf(c);
        }
        Arrays.sort(b);
        if (b[a.length() - 1] == -1) {
            max = 0;
        } else {
            max = b[a.length() - 1];
        }
        if (pending.indexOf(".", max) == -1) {
            return true;
        } else {
            return false;
        }
    }


}