import java.util.ArrayList;import java.util.List;// 辅助类class Item{    String value;    boolean isNumber;        public Item(String value,boolean isNumber){        this.value=http://www.mamicode.com/value;        this.isNumber=isNumber;    }        public Item(char c,boolean isNumber){        this.value=http://www.mamicode.com/String.valueOf(c);        this.isNumber=isNumber;    }        public String toString(){        return ""+value+" & "+isNumber;    }}/** * 算术表达式求值 */public class ArithCaculator{    private String line;// 输入的算式    private String result;// 计算得到的结果        public ArithCaculator(String line){        this.line=line;        int length=line.length();

        // 得到包含数字和操作符的列表        List<Item> ls=new ArrayList<Item>();        String str="";        for(int i=0;i<length;i++){            char ch=line.charAt(i);                        if((ch>=‘0‘ && ch<=‘9‘) || ch==‘.‘){                str+=ch;            }else if(ch==‘+‘ || ch==‘-‘ || ch==‘*‘ || ch==‘/‘ || ch==‘(‘ || ch==‘)‘ ){                if(str.length()>0){                    ls.add(new Item(str,true));                    str="";                }                                ls.add(new Item(ch,false));            }                        if(i==length-1 && str.length()>0){                ls.add(new Item(str,true));            }        }                // 得到后序表达式        ls=getPostfix(ls);                // 计算后序表达式        this.result=getValue(ls);    }        // 对后序表达式进行计算    private String getValue(List<Item> ls){        Stack<Item> stack=new Stack<Item>(Item.class,ls.size());        double result;                for(Item it:ls){            if(it.isNumber){                stack.push(it);            }else{                // 栈先进后出所以颠倒                double op2=Double.parseDouble(stack.pop().value);                double op1=Double.parseDouble(stack.pop().value);                                result=0;                char ch=it.value.charAt(0);                                if(ch==‘+‘){                    result=op1+op2;                }else if(ch==‘-‘){                    result=op1-op2;                }else if(ch==‘*‘){                    result=op1*op2;                }else if(ch==‘/‘){                    result=op1/op2;                }                                stack.push(new Item(String.valueOf(result),true));            }        }                return stack.pop().value;    }        // 得到后序表达式    private List<Item> getPostfix(List<Item> ls){        List<Item> retval=new ArrayList<Item>();        Stack<Character> stack=new Stack<Character>(Character.class,ls.size());                for(Item it:ls){            if(it.isNumber){                retval.add(it);            }else{                if("+".equals(it.value) || "-".equals(it.value) ){                    gotOper(stack,retval,it.value,1);                }else if("*".equals(it.value) || "/".equals(it.value) ){                    gotOper(stack,retval,it.value,2);                }else if("(".equals(it.value)){                    stack.push(‘(‘);                }else if(")".equals(it.value)){                    gotParen(stack,retval,‘)‘);                }            }        }                while(stack.isEmpty()==false){            retval.add(new Item(stack.pop(),false));        }                return retval;    }        private void gotOper(Stack<Character> stack,List<Item> ls,String opThis,int prec){        while(stack.isEmpty()==false){            char opTop=stack.pop();                        if(opTop==‘(‘){                stack.push(opTop);                break;            }else{                int prec2=2;                                if(opTop==‘+‘ || opTop==‘-‘){                    prec2=1;                }                                if(prec2<prec){                    stack.push(opTop);                    break;                }else{                    ls.add(new Item(opTop,false));                }            }        }                stack.push(opThis.charAt(0));    }        private void gotParen(Stack<Character> stack,List<Item> ls,char ch){        while(stack.isEmpty()==false){            char chTop=stack.pop();                        if(chTop==‘(‘){                break;            }else{                ls.add(new Item(chTop,false));            }        }    }        public String getLine() {        return line;    }    public String getResult() {        return result;    }        public static void main(String[] args){        String[] arr=new String[]{"2+3+5","2+(3*5)-6","4+5*(1+2)","1*2+3*4","(3+4)*5/2+33","5+17+12.5","8.0/(3.0-(8.0/3.0))","((10.0*10.0)-4.0)/4.0"};                for(String str:arr){            ArithCaculator a=new ArithCaculator(str);            System.out.println(a.getLine()+"="+a.getResult());        }    }}

2+3+5=10.02+(3*5)-6=11.04+5*(1+2)=19.01*2+3*4=14.0(3+4)*5/2+33=50.55+17+12.5=34.58.0/(3.0-(8.0/3.0))=23.99999999999999((10.0*10.0)-4.0)/4.0=24.0