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详细对一般字符串表达式解析

                                
                        b<I>.setBackground(Color.lightGray);<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        b<I>.setForeground(Color.blue);<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; <BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; for(int 
                        i=4;i&lt;15;i=i+5)<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        {<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        b<I>.setBackground(Color.lightGray);<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        b<I>.setForeground(Color.red); <BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; <BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; for(int i=17;i&lt;21;i++)<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; 
                        b<I>.setBackground(Color.lightGray);<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        b<I>.setForeground(Color.blue);<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; <BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; for(int i=19;i&lt;21;i++)<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; 
                        b<I>.setBackground(Color.lightGray);<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        b<I>.setForeground(Color.red);<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; <BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; for(int i=1;i&lt;4;i++)<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; 
                        b[i*5].setBackground(Color.lightGray);<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        b[i*5].setForeground(Color.blue);<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        <BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        f.add(tf,"North");<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        p.add(p1,"Center");<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        p.add(p2,"North");<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        p.add(p3,"West");<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        f.add(p,"Center");<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        f.pack();<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        f.setResizable(false);<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        f.setVisible(true);<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        f.addWindowListener(new WindowAdapter()<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; public void windowClosing(WindowEvent 
                        e)<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        {<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; System.exit(1);<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; } <BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        });<BR>&nbsp; &nbsp; }<BR>&nbsp; &nbsp; <BR>&nbsp; 
                        &nbsp; public void actionPerformed(ActionEvent 
                        e)<BR>&nbsp; &nbsp; {&nbsp; &nbsp; <BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; s = e.getActionCommand();<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; String s1 = tf.getText();<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; <BR><BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        if(s=="0"|s=="1"|s=="2"|s=="3"|s=="4"|s=="5"|s=="6"|s=="7"|s=="8"|s=="9")<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; if(flag)<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; tf.setText(s1 + s);<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; else<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; tf.setText(s);<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; flag = 
                        true;<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        }<BR>&nbsp; &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; <BR>&nbsp; &nbsp; &nbsp; &nbsp; else 
                        if(s=="+"|s=="-"|s=="*"|s=="/")<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        result = Double.parseDouble(s1);<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; flag = false;<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; oper = s;<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        <BR>&nbsp; &nbsp; &nbsp; &nbsp; else 
                        if(s=="=")<BR>&nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; tmp1 = 
                        Double.parseDouble(tf.getText());<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; if(oper == "+") result += 
                        tmp1;<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        if(oper == "-") result -= tmp1;<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; if(oper == "*") result *= 
                        tmp1;<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        if(oper == "/") result /= tmp1;<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; 
                        tf.setText(Double.toString(result));<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; oper = "";<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; flag = false;<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        <BR>&nbsp; &nbsp; &nbsp; &nbsp; else 
                        if(s=="+/-")<BR>&nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; tmp2 = 
                        -1*Double.parseDouble(tf.getText());<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        tf.setText(Double.toString(tmp2));<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        <BR>&nbsp; &nbsp; &nbsp; &nbsp; else 
                        if(s=="sqrt")<BR>&nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; tmp3 = 
                        Double.parseDouble(tf.getText());<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; if(tmp3&gt;0)<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; tmp3 = 
                        Math.sqrt(tmp3);<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; 
                        tf.setText(Double.toString(tmp3));<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; flag = 
                        false;<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        }<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        else{}<BR>&nbsp; &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; <BR>&nbsp; &nbsp; &nbsp; &nbsp; else 
                        if(s=="1/x")<BR>&nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; tmp4 = 
                        1/Double.parseDouble(tf.getText());<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        tf.setText(Double.toString(tmp4));<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; flag = false;<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        <BR>&nbsp; &nbsp; &nbsp; &nbsp; else 
                        if(s=="%")<BR>&nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; tmp5 = 
                        Double.parseDouble(tf.getText())/100;<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; if(oper == "*")<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; result = 
                        result*(result*tmp5);<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        tf.setText(Double.toString(result));<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; else if(oper == "+")<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; result = 
                        result+result*tmp5;<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        tf.setText(Double.toString(result));<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; else if(oper == "-")<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; result = 
                        result-result*tmp5;<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        tf.setText(Double.toString(result));<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; else if(oper == "/")<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; result = 
                        result/(result*tmp5);<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; 
                        tf.setText(Double.toString(result));<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; else<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; tf.setText("0.0");<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; flag = false;<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; oper = "";<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        <BR>&nbsp; &nbsp; &nbsp; &nbsp; else if(s=="&nbsp; 
                        退格&nbsp; ")<BR>&nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; String after = 
                        s1.substring(0,(s1.length()-1));<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; tf.setText(after);<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        <BR>&nbsp; &nbsp; &nbsp; &nbsp; else 
                        if(s==".")<BR>&nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        if(s1.indexOf('.')==-1)<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; {<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; tf.setText(s1+s);<BR>&nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; 
                        &nbsp; &nbsp; &nbsp; else{}&nbsp; &nbsp; <BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; }<BR>&nbsp; &nbsp; &nbsp; &nbsp; 
                        <BR>&nbsp; &nbsp; &nbsp; &nbsp; else if(s=="&nbsp; 
                        &nbsp; CE&nbsp; &nbsp; "|s=="&nbsp; &nbsp; C&nbsp; 
                        &nbsp; ")<BR>&nbsp; &nbsp; &nbsp; &nbsp; {<BR>&nbsp; 
                        &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        tf.setText("0");<BR>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
                        &nbsp; flag = false;<BR>&nbsp; &nbsp; &nbsp; &nbsp;