实验一：做一个简单的计算器
1.创建布局文件Activity_main.xml
代码如下：
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="/apk/res/android"android:orientation="vertical"android:layout_width="match_parent"android:layout_height="match_parent"><EditTextandroid:id="@+id/result"android:layout_width="match_parent"android:layout_height="wrap_content"android:textSize="40sp"android:enabled="false"/><LinearLayoutandroid:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:orientation="horizontal"><Buttonandroid:id="@+id/cls"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="C"android:textColor="#ffffff"/><Buttonandroid:id="@+id/div"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="/"android:textColor="#ffffff"/><Buttonandroid:id="@+id/mul"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="*"android:textColor="#ffffff"/><Buttonandroid:id="@+id/Backspace"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="Backspace"android:textAllCaps="false"android:textColor="#ffffff"/></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:orientation="horizontal"><Buttonandroid:id="@+id/seven"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="7"android:textColor="#ffffff"/><Buttonandroid:id="@+id/eight"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="8"android:textColor="#ffffff"/><Buttonandroid:id="@+id/nine"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="9"android:textColor="#ffffff"/><Buttonandroid:id="@+id/sub"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="-"android:textColor="#ffffff"/></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:orientation="horizontal"><Buttonandroid:id="@+id/four"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="4"android:textColor="#ffffff"/><Buttonandroid:id="@+id/five"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="5"android:textColor="#ffffff"/><Buttonandroid:id="@+id/six"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="6"android:textColor="#ffffff"/><Buttonandroid:id="@+id/add"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="+"android:textColor="#ffffff"/></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="2"android:orientation="horizontal"><LinearLayoutandroid:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:orientation="vertical"><LinearLayoutandroid:layout_width="match_parent"android:layout_height="1dp"android:layout_weight="1"android:orientation="horizontal"><Buttonandroid:id="@+id/one"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="1"android:textColor="#ffffff"/><Buttonandroid:id="@+id/two"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:textSize="20sp"android:text="2"android:textColor="#ffffff"/></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="1dp"android:layout_weight="1"><Buttonandroid:id="@+id/zero"android:layout_width="match_parent"android:layout_height="match_parent"android:text="0"android:textSize="20sp"android:textColor="#ffffff"/></LinearLayout></LinearLayout><LinearLayoutandroid:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:orientation="horizontal"><LinearLayoutandroid:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:orientation="vertical"><Buttonandroid:id="@+id/three"android:layout_width="match_parent"android:layout_height="1dp"android:layout_weight="1"android:text="3"android:textSize="20sp"android:textColor="#ffffff"/><Buttonandroid:id="@+id/spot"android:layout_width="match_parent"android:layout_height="1dp"android:layout_weight="1"android:text="."android:textSize="20sp"android:textColor="#ffffff"/></LinearLayout><LinearLayoutandroid:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"><Buttonandroid:id="@+id/equal"android:layout_width="match_parent"android:layout_height="match_parent"android:text="="android:textSize="20sp"android:textColor="#ffffff"/></LinearLayout></LinearLayout></LinearLayout></LinearLayout>
2.创建Java文件ActivityMain.java
代码如下：
package com.example.a86761.zdj003; #换自己的工程名import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.view.View;import android.widget.Button;import android.widget.EditText;import java.lang.reflect.Method;import java.math.BigDecimal;import java.util.ArrayList;import java.util.List;public class MainActivity extends AppCompatActivity{private StringBuilder show_equation=new StringBuilder();//显示运算式private ArrayList calculate_equation;//计算式private int signal=0;//为0 时表示刚输入状态；为1 时表示当前在输出结果上继续输入@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//初始化show_equation=new StringBuilder();calculate_equation=new ArrayList<>();Button zero=(Button)findViewById(R.id.zero);Button one=(Button)findViewById(R.id.one);Button two=(Button)findViewById(R.id.two);Button three=(Button)findViewById(R.id.three);Button four=(Button)findViewById(R.id.four);Button five=(Button)findViewById(R.id.five);Button six=(Button)findViewById(R.id.six);Button seven=(Button)findViewById(R.id.seven);Button eight=(Button)findViewById(R.id.eight);Button nine=(Button)findViewById(R.id.nine);Button cls=(Button)findViewById(R.id.cls);Button div=(Button)findViewById(R.id.div);Button mul=(Button)findViewById(R.id.mul);Button backspace=(Button)findViewById(R.id.Backspace);Button sub=(Button)findViewById(R.id.sub);Button add=(Button)findViewById(R.id.add);final Button equal=(Button)findViewById(R.id.equal);final Button point=(Button)findViewById(R.id.spot);final EditText result=(EditText)findViewById(R.id.result);result.setCursorVisible(true);disableShowInput(result);//点击文本框时光标始终在文本末尾result.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View view) {result.setSelection(result.getText().length());}});zero.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v){if(!(show_equation.toString().equals("0"))){if(signal==0){show_equation.append("0");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("0");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}}});one.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){show_equation.append("1");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("1");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}});two.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){show_equation.append("2");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("2");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}});three.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){show_equation.append("3");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("3");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}});four.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){show_equation.append("4");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("4");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}});five.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){show_equation.append("5");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("5");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}});six.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){show_equation.append("6");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("6");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}});seven.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){show_equation.append("7");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("7");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}});eight.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){show_equation.append("8");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("8");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}});nine.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){show_equation.append("9");result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());show_equation.append("9");result.setText(show_equation);result.setSelection(result.getText().length());signal=0;}}});cls.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {show_equation.delete(0,show_equation.length());calculate_equation.clear();signal=0;result.setText("");}});backspace.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(!(show_equation.toString().equals(""))) {if(signal==0){show_equation.deleteCharAt(show_equation.length() - 1);result.setText(show_equation);result.setSelection(result.getText().length());}else{show_equation.delete(0,show_equation.length());result.setText("");signal=0;}}}});point.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if(signal==0){String a=show_equation.toString();if(a.equals("")){show_equation.append(".");result.setText(show_equation);result.setSelection(result.getText().length());}else{int i;char t='0';for(i=a.length();i>0;i--){t=a.charAt(i-1);if(t=='.'||t=='+'||t=='-'||t=='*'||t=='/')break;}if(i==0){show_equation.append(".");result.setText(show_equation);result.setSelection(result.getText().length());}else if(t=='+'||t=='-'||t=='*'||t=='/'){show_equation.append(".");result.setText(show_equation);result.setSelection(result.getText().length());}}}else{show_equation.delete(0,show_equation.length());show_equation.append(".");result.setText(".");result.setSelection(result.getText().length());signal=0;}}});equal.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//判断用户是否输入了内容if(!show_equation.toString().equals("")){signal=1;char temp=show_equation.charAt(show_equation.length()-1);if(show_equation.charAt(0)=='-')show_equation.insert(0,"0");if(temp=='+'||temp=='-')show_equation.append("0");if(temp=='*'||temp=='/')show_equation.append("1");StringBuilder temp1=new StringBuilder();for(int i=0;i<show_equation.length();i++){if(show_equation.charAt(i)>='0'&&show_equation.charAt(i)<='9'||show_equation.charAt(i)=='.'){temp1.append(String.valueOf(show_equation.charAt(i)));}else if(show_equation.charAt(i)=='N'){calculate_equation.add("NaN");//跳过2个字符i=i+2;}else if(show_equation.charAt(i)=='∞'){calculate_equation.add("∞");}else{if(temp1.length()!=0){calculate_equation.add(temp1.toString());temp1.delete(0,temp1.length());}calculate_equation.add(String.valueOf(show_equation.charAt(i)));}}if(temp1.length()!=0){calculate_equation.add(temp1.toString());}calculate_equation.add("#");String temp8=calculate(calculate_equation);result.setText(temp8);result.setSelection(result.getText().length());show_equation.delete(0,show_equation.length());calculate_equation.clear();show_equation.append(temp8);}}});add.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//判断用户是否输入了内容if(!(show_equation.toString().equals(""))) {signal=0;char temp=show_equation.charAt(show_equation.length()-1);if(temp=='+'||temp=='-'||temp=='*'||temp=='/'){show_equation.deleteCharAt(show_equation.length()-1);show_equation.append("+");}elseshow_equation.append("+");result.setText(show_equation);result.setSelection(result.getText().length());}}});sub.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//判断用户是否输入了内容if(!(show_equation.toString().equals(""))) {signal=0;char temp=show_equation.charAt(show_equation.length()-1);if(temp=='+'||temp=='-'||temp=='*'||temp=='/'){show_equation.deleteCharAt(show_equation.length()-1);show_equation.append("-");}elseshow_equation.append("-");result.setText(show_equation);result.setSelection(result.getText().length());}}});mul.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//判断用户是否输入了内容if(!(show_equation.toString().equals(""))) {signal=0;char temp=show_equation.charAt(show_equation.length()-1);if(temp=='+'||temp=='-'||temp=='*'||temp=='/'){show_equation.deleteCharAt(show_equation.length()-1);show_equation.append("*");}elseshow_equation.append("*");result.setText(show_equation);result.setSelection(result.getText().length());}}});div.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//判断用户是否输入了内容if(!(show_equation.toString().equals(""))) {signal=0;char temp=show_equation.charAt(show_equation.length()-1);if(temp=='+'||temp=='-'||temp=='*'||temp=='/'){show_equation.deleteCharAt(show_equation.length()-1);show_equation.append("/");}elseshow_equation.append("/");result.setText(show_equation);result.setSelection(result.getText().length());}}});}protected boolean operatorPriorityCompare(char operator1,char operator2){int o1=0;int o2=0;switch (operator1){case '+':{o1=0;break;}case '-':{o1=0;break;}case '*':{o1=1;break;}case '/':{o1=1;break;}}switch (operator2){case '+':{o2=0;break;}case '-':{o2=0;break;}case '*':{o2=1;break;}case '/':{o2=1;break;}}if(o1<=o2){return false;}elsereturn true;}//相加public static Double Add(Double d1,Double d2) {if(d1==Double.NEGATIVE_INFINITY||d1==Double.POSITIVE_INFINITY||d2==Double.NEGATIVE_INFINITY||d2==Double.POSITIVE_INFINITY){return d1+d2;}if(String.valueOf(d1).equals("NaN")||String.valueOf(d1).equals("NaN")){return d1+d2;}BigDecimal b1 = new BigDecimal(Double.toString(d1));BigDecimal b2 = new BigDecimal(Double.toString(d2));return b1.add(b2).doubleValue();}//相减public static Double Sub(Double d1,Double d2){if(d1==Double.NEGATIVE_INFINITY||d1==Double.POSITIVE_INFINITY||d2==Double.NEGATIVE_INFINITY||d2==Double.POSITIVE_INFINITY){return d1-d2;}if(String.valueOf(d1).equals("NaN")||String.valueOf(d1).equals("NaN")){return d1-d2;}if(String.valueOf(d1).equals("NaN")||String.valueOf(d1).equals("NaN")){return d1*d2;}BigDecimal b1=new BigDecimal(Double.toString(d1));BigDecimal b2=new BigDecimal(Double.toString(d2));return b1.subtract(b2).doubleValue();}//相乘public static Double Mul(Double d1,Double d2){if(d1==Double.NEGATIVE_INFINITY||d1==Double.POSITIVE_INFINITY||d2==Double.NEGATIVE_INFINITY||d2==Double.POSITIVE_INFINITY){return d1*d2;}if(String.valueOf(d1).equals("NaN")||String.valueOf(d1).equals("NaN")){return d1*d2;}BigDecimal b1=new BigDecimal(Double.toString(d1));BigDecimal b2=new BigDecimal(Double.toString(d2));return b1.multiply(b2).setScale(8).doubleValue();}//相除public static Double Div(Double d1,Double d2){if(d1==Double.NEGATIVE_INFINITY||d1==Double.POSITIVE_INFINITY||d2==Double.NEGATIVE_INFINITY||d2==Double.POSITIVE_INFINITY){return d1/d2;}if(String.valueOf(d1).equals("NaN")||String.valueOf(d1).equals("NaN")){return d1/d2;}if(d1==0.0&&d2==0.0){return Double.NaN;}if(d2==0.0){return d1/d2;}BigDecimal b1=new BigDecimal(Double.toString(d1));BigDecimal b2=new BigDecimal(Double.toString(d2));return b1.divide(b2,8,BigDecimal.ROUND_HALF_UP).doubleValue();}protected String calculate(ArrayList equation){Double temp2;Double temp3;Double result;List operator=new ArrayList();List<Double> operand=new ArrayList();for(int i=0;i<equation.size();i++){String temp4=(String) equation.get(i);if(temp4.equals("+")||temp4.equals("-")||temp4.equals("*")||temp4.equals("/")){if(operator.size()>0){String temp5=operator.get(operator.size()-1).toString();while(!(operatorPriorityCompare(temp4.charAt(0),temp5.charAt(0)))&&operator.size()>0){operator.remove(operator.size()-1);temp3=operand.get(operand.size()-1);operand.remove(operand.size()-1);temp2=operand.get(operand.size()-1);operand.remove(operand.size()-1);switch (temp5.charAt(0)){case '+':{result=Add(temp2,temp3);operand.add(result);break;}case '-':{result=Sub(temp2,temp3);operand.add(result);break;}case '*':{result=Mul(temp2,temp3);operand.add(result);break;}case '/':{result=Div(temp2,temp3);operand.add(result);break;}}if(operator.size()>0){temp5=operator.get(operator.size()-1).toString();}elsebreak;}operator.add(temp4);}elseoperator.add(temp4);}else if(temp4.equals("#")){while(operator.size()>0){String temp6=(String)operator.get(operator.size()-1);operator.remove(operator.size()-1);temp3=operand.get(operand.size()-1);operand.remove(operand.size()-1);temp2=operand.get(operand.size()-1);operand.remove(operand.size()-1);switch (temp6.charAt(0)){case '+':{result=Add(temp2,temp3);operand.add(result);break;}case '-':{result=Sub(temp2,temp3);operand.add(result);break;}case '*':{result=Mul(temp2,temp3);operand.add(result);break;}case '/':{result=Div(temp2,temp3);operand.add(result);break;}}}}else{if(temp4.equals("NaN")){operand.add(Double.NaN);}else if(temp4.equals("∞")){operand.add(Double.POSITIVE_INFINITY);}else{operand.add(Double.parseDouble(temp4));}}}if(operand.get(0)==Double.NEGATIVE_INFINITY) return "-∞";if(operand.get(0)==Double.POSITIVE_INFINITY) return "∞";return operand.get(0).toString();}//当API最低版小于21时使用这个函数实现点击文本框不弹出键盘public void disableShowInput(EditText et) {Class<EditText> cls = EditText.class;Method method;try {method = cls.getMethod("setShowSoftInputOnFocus", boolean.class);method.setAccessible(true);method.invoke(et, false);} catch (Exception e) {e.printStackTrace();}}}
运行截图：
