JAVA学习日报 10/14

今天时10月14号，星期三

特别尝试了一下四则运算中分数和小数的计算……先说结论——果然不行啊，字符串读入读小数会报一个叫NullPointerException的奇妙异常

解决了好一阵也没能彻底解决……啊，放弃！

欸……话说下次的四则运算会不会就是小数了啊……

另外虽然是失败作品……不过也把代码贴上来吧

public static String getzongde(String str){
            String kuohao=getkuohao(str);
            String chengchu=getchengchu(kuohao);
            String jiajian=getjiajian(chengchu);
            return jiajian;
        }
        public static String getkuohao(String str){
            String newstr=str;
            if(newstr.contains("(")){
                int a=str.lastIndexOf("(");
                String str1=str.substring(a,str.length());
                int b =str1.indexOf(")");
                String str2=str1.substring(1,b);
                String chengchu=getchengchu(str2);
                String jiajian=getjiajian(chengchu);
                StringBuffer s=new StringBuffer(str);
                newstr=s.replace(a, a+b+1, jiajian).toString();
                return getkuohao(newstr);
                
            }
            return newstr;
        }
        public static String getchengchu(String str){
            String newstr=str;
            if(str.contains("*")||str.contains("/")){
                String str2[]=str.split("[*/+-]");//
                String str3=str.replaceAll("\\d+","").replaceAll("\\.","");
                int a=0,b=0,c=0,star=0;
                if(str3.contains("*")&&str3.contains("/")){
                    a=str3.indexOf("*");
                    b=str3.indexOf("/");
                    if(a>b){
                        c=b;    
                        star=str.indexOf("/");
                    }else{
                        c=a;
                        star=str.indexOf("*");
                    }
                }else if(str3.contains("*")){
                    c=str3.indexOf("*");
                    star=str.indexOf("*");
                }else{
                    c=str3.indexOf("/");
                    star=str.indexOf("/");
                }
                String num=getsuanshi(str2[c]+str3.charAt(c)+str2[c+1]);
                StringBuffer s=new StringBuffer(str);
                int kaishi=star-str2[c].length(),jieshu=star+str2[c+1].length()+1;
                StringBuffer strs=s.replace(kaishi,jieshu ,num);
                newstr=strs.toString();
                return getchengchu(newstr);
            }
            return newstr;
        }
        public static String getjiajian(String str){
            String newstr=str;
            if(str.contains("+")||str.contains("-")){
                String str2[]=str.split("[*/+-]");
                String str3=str.replaceAll("\\d+","").replaceAll("\\.","");
                int a=0,b=0,c=0,star=0;
                if(str3.contains("+")&&str3.contains("-")){
                    a=str3.indexOf("+");
                    b=str3.indexOf("-");
                    if(a>b){
                        c=b;    
                        star=str.indexOf("-");
                    }else{
                        c=a;
                        star=str.indexOf("+");
                    }
                }else if(str3.contains("+")){
                    c=str3.indexOf("+");
                    star=str.indexOf("+");
                }else{
                    c=str3.indexOf("-");
                    star=str.indexOf("-");
                }
                String num=getsuanshi(str2[c]+str3.charAt(c)+str2[c+1]);
                StringBuffer s=new StringBuffer(str);
                int kaishi=star-str2[c].length(),jieshu=star+str2[c+1].length()+1;
                StringBuffer strs=s.replace(kaishi,jieshu ,num);
                newstr=strs.toString();
                return getjiajian(newstr);
            }
            return newstr;
        }
        public static String getsuanshi(String str){
            double c=0.0;
            String str2[];
            if(str.contains("+")){
                str2=str.split("[+]");
                c=getjia(Double.parseDouble(str2[0]),Double.parseDouble(str2[1]));
            }else if(str.contains("-")){
                str2=str.split("[-]");
                c=getjian(Double.parseDouble(str2[0]),Double.parseDouble(str2[1]));
            }else if(str.contains("*")){
                str2=str.split("[*]");
                c=getcheng(Double.parseDouble(str2[0]),Double.parseDouble(str2[1]));
            }else if(str.contains("/")){
                str2=str.split("[/]");
                c=getchu(Double.parseDouble(str2[0]),Double.parseDouble(str2[1]));
            }
            NumberFormat format=NumberFormat.getInstance();
            format.setMaximumFractionDigits(30);
            format.setMinimumFractionDigits(0);
            format.setGroupingUsed(false);
            return format.format(c);
        }
        public static Double getjia(double a,double b){
            double c=a+b;
            return c;
        }
        public static Double getjian(double a,double b){
            double c=a-b;
            return c;
        }
        public static Double getcheng(double a,double b){
            double c=a*b;
            return c;
        }
        public static Double getchu(double a,double b){
            double c=a/b;
            return c;
        }

好，今天就是这样啦