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/**
* 1.先转换为逆波兰顺序
* 数字直接存入list,符号压入栈中,但是如果栈底元素不大于该运算符的运算顺序,则将栈底pop,直到大于栈底运算符为止,再压入栈中,
* 最后将运算符依次全部pop(以上pop出的运算符存入list)
* 2.根据逆序算出结果
* 从头到尾依次读取list的数据,将数字压入栈中,出现运算符后pop出两个数字进行运算,运算式为"后pop数 运算符 先pop数"
* 运算完毕将结果再次压入栈中.结束后,将数字栈中的唯一一个数字pop出并将其返回.
*
*
* 学习之处:
* 1.String对象的比较不要用==,>,<.>
* 2.使用HashMap()的定义可以给对象进行编号或加权.
* 3.需要时要给读取的信息加上结尾标志,如读入String结尾的"#".
* 4.取String的单个字母:String temps=String.valueOf(expression.charAt(i));
* 5.检测数字:temps.matches("[0-9.]")
**/
1 public classCalculator {2 privateString string;3 private MyStack opratorStack = newMyStack();4 private MyStack numberStack = newMyStack();5 private ArrayList rpnList = newArrayList();6 private Map priorityMap=new HashMap();//用于存储操作符优先级的Map7 //初始化优先级约定(可根据计算的复杂程度扩展)
8
9 publicCalculator(String str)10 {11 priorityMap.put("+",0);12 priorityMap.put("-",0);13 priorityMap.put("*", 1);14 priorityMap.put("/", 1);15 priorityMap.put("(", 2);16 string = str+"#";17 }18 private int getPriority(String op)//得到一个操作符的优先级
19 {20 returnpriorityMap.get(op);21 }22
23 private voidtoRpn() {24
25 String temp = "";26 for (int i = 0; i < string.length(); i++) {27 String ch =String.valueOf(string.charAt(i));28 if (ch.matches("[0-9.]"))29 temp +=ch;30
31 else { //如果操作数完整,现将其存入list中再进行后续操作
32
33 if(!temp.equals("")) {//防止加入进空格
34 rpnList.add(temp);35 temp = "";36 }37
38 if (ch.equals("#")) { //读取结束时将运算符栈依次pop并添加到rpnList中
39 while (!opratorStack.isEmpty()) {40 rpnList.add(opratorStack.pop());41 }42 } else if (ch.equals(")")) { //遇到右括号将左括号后的运算符全部pop
43 String op =opratorStack.pop();44 while (!op .equals("(")) {45 rpnList.add(op);46 op =opratorStack.pop();47 }48 } else{49 if (!opratorStack.isEmpty()) { //如果为普通的运算符
50 String endOprator =opratorStack.endValue();51
52 while (!endOprator.equals( "(") && (getPriority(ch)
55 if (!opratorStack.isEmpty()) {56 endOprator =opratorStack.endValue();57 }else
58 break;59
60 }61
62 opratorStack.push(ch);63 }64 else
65 opratorStack.push(ch);66 }67 }68 }69 }70
71 public doublecalculate(String string){72 this.string = string+"#";73 returncalculate();74 }75
76 public doublecalculate(){77 toRpn();//逆波兰序列转换78
79 //扫描String对象
80 for(int i = 0; i < rpnList.size(); i++){81 String temp =rpnList.get(i);82 //匹配第一个字符,为数字的则将String对象转为Double并存入numberStack中
83 if(String.valueOf(temp.charAt(0)).matches("[0-9]")){84 numberStack.push(Double.valueOf(temp));85 } //匹配到运算符,调出最后两个numberStack中数字进行运算,并将得数压入栈中(栈次底数 操作符 栈最底数)
86 else{87 //Double n = opration(numberStack.pop(), numberStack.pop(), temp);
88 Double n =numberStack.pop();89 numberStack.push(opration(numberStack.pop(), n , temp));90 }91 }92
93 rpnList = new ArrayList();//为下次运算做准备
94 returnnumberStack.pop();95 }96
97 privateDouble opration(Double val1,Double val2,String oprator){98 if(oprator.equals("+"))99 val1 +=val2;100 else if(oprator.equals("-"))101 val1 -=val2;102 else if(oprator.equals("*"))103 val1 *=val2;104 else
105 val1 /=val2;106 returnval1;107 }108
109 public static voidmain(String[] args) {110 String string1 = "12+2*37-(4*5+6)*7";111 Calculator calculator = newCalculator(string1);112
113 System.out.println(calculator.calculate());114 System.out.println(calculator.calculate("4.99+5.99+6.99*1.06"));115 }116 }
运算结果:
-96.0
18.389400000000002
Process finished with exit code 0