在進(jìn)行一個(gè)表達(dá)式的計(jì)算時(shí)，先將表達(dá)式分割成數(shù)字和字符串然后利用出入棧將分割后的表達(dá)式進(jìn)行中綴轉(zhuǎn)后綴，再將后綴表達(dá)式進(jìn)行計(jì)算得到結(jié)果(思想在上一篇寫(xiě)過(guò))現(xiàn)在貼下Java語(yǔ)言的代碼實(shí)現(xiàn)。(學(xué)習(xí)Java時(shí)間不長(zhǎng)所以可能會(huì)有很多不足的地方，我會(huì)改進(jìn)也歡迎大神可以給我一些意見(jiàn)和建議~謝謝啦)
我將這部分分成三個(gè)方法完成功能，并在getResult方法調(diào)用(getResult方法被主方法調(diào)用)
private String getResult(String str) { //分割 String[] Str = segment(str); //中綴轉(zhuǎn)后綴 String newStr = infToSuf(Str); //后綴計(jì)算 String result = sufToRes(newStr); return sufToRes(result); }1.字符串分割，為避免在TextView上顯示帶空格刪除時(shí)不方便而且顯示屏就那么大占地方，錄入時(shí)的字符串中沒(méi)有空格然后就手動(dòng)分割了
private static String[] segment(String str) { String[] exp = new String[str.length()+1]; //找最近的索引并截取字符串 int l = str.length(); for(int i = 0;i < l+1;i++) { int index; int[] ind = new int[6]; ind[0] = str.indexOf('+'); ind[1] = str.indexOf('-'); ind[2] = str.indexOf('*'); ind[3] = str.indexOf('/'); ind[4] = str.indexOf('('); ind[5] = str.indexOf(')'); if(ind[1] == 0) { Arrays.sort(ind); int t; for(t = 0;t <6;t++) { if(ind[t] >= 0) break; } int r = ind[t+1]; exp[i] = str.substring(0,r); i++; exp[i] = str.substring(r,r+1); str = str.substring(r+1); }else if(((ind[1]-ind[4]) == 1) && (ind[4]==0)) { Arrays.sort(ind); int t ; for(t = 0;t <6;t++) { if(ind[t] >= 0) break; } int r = ind[t+1]; exp[i] = str.substring(0,1); i++; exp[i] = str.substring(1,r+2); i++; exp[i] = str.substring(r+2,r+3); str = str.substring(r+3); }else { Arrays.sort(ind); int t; for(t = 0;t <6;t++) { if(ind[t] >= 0) break; } if(t==6) break; index = ind[t]; if(index!=0) { exp[i] = str.substring(0,index); i++; } exp[i] = str.substring(index,index+1); str = str.substring(index+1); } } int j = 0; int k = 0; for(; exp[j]!=null ;j++){} if(!exp[j-1].equals(")")) { exp[j]=str; str = ""; k = j; }else { k = j-1; } String[] expp = new String[k+1]; for(int t = 0; t < k+1;t++) { expp[t] = exp[t]; } return expp; //System.out.println("分割的字符串:"); }2.中綴轉(zhuǎn)后綴
private static String infToSuf(String[] exp) { String newStrs = ""; //初始化棧 Stack<String> stack = new Stack<>(); /* 判斷并放入后綴表達(dá)式中： for循環(huán)遍歷整個(gè)str進(jìn)行判斷 循環(huán)結(jié)束若棧不為空全部出棧 */ int l = exp.length; for(int i = 0; i < l; i++) { if ((stack.empty()) && (exp[i].equals("+") || exp[i].equals("-") || exp[i].equals("*") || exp[i].equals("/"))) { stack.push(exp[i]); } else if (exp[i].equals("(")) { stack.push(exp[i]); } else if (exp[i].equals("*") || exp[i].equals("/")) { while (stack.peek().equals("*") || stack.peek().equals("/")) { newStrs = newStrs.concat(stack.pop()+" "); if(stack.isEmpty()) { break; } } stack.push(exp[i]); } else if (exp[i].equals("+") || exp[i].equals("-")) { while (!(stack.isEmpty())&&((stack.peek()).equals("*") || (stack.peek()).equals("/") || (stack.peek()).equals("+") || (stack.peek()).equals("-"))) { newStrs = newStrs.concat(stack.pop()+" "); if(stack.isEmpty()) { break; } } stack.push(exp[i]); } else if (exp[i].equals(")")) { int t = stack.search("("); for (int k = 1; k < t; k++) { newStrs = newStrs.concat(stack.pop()+" "); } String tstr = stack.pop(); } else { newStrs = newStrs.concat(exp[i]+ " "); } } while (!stack.empty()) { if (!stack.peek().equals("(") || !stack.peek().equals(")")) { newStrs = newStrs.concat(stack.pop()+" "); } else if (stack.peek().equals("(") || stack.peek().equals(")")) { String tstr = stack.pop(); } }// System.out.println("后綴:"+newStrs); return newStrs; }3.后綴的計(jì)算
private static String sufToRes(String sufStr) { String[] exp = sufStr.split(" "); Stack<String> stack = new Stack<>(); String Res = ""; for(int i = 0;i < exp.length; i++) { if(!exp[i].equals("+") && !exp[i].equals("-") && !exp[i].equals("*") && !exp[i].equals("/")){ stack.push(exp[i]); }else if(exp[i].equals("+")) { BigDecimal b2 = new BigDecimal(stack.pop()); BigDecimal b1 = new BigDecimal(stack.pop()); BigDecimal b3 = b1.add(b2); stack.push(b3.toString()); }else if(exp[i].equals("-")) { BigDecimal b2 = new BigDecimal(stack.pop()); BigDecimal b1 = new BigDecimal(stack.pop()); BigDecimal b3 = b1.subtract(b2); stack.push(b3.toString()); }else if(exp[i].equals("*")) { BigDecimal b2 = new BigDecimal(stack.pop()); BigDecimal b1 = new BigDecimal(stack.pop()); BigDecimal b3 = new BigDecimal(0); if(b1.compareTo(BigDecimal.ZERO)== 0|| b2.compareTo(BigDecimal.ZERO) == 0) { b3 = BigDecimal.ZERO; }else { b3 = b1.multiply(b2); } stack.push(b3.toString()); }else if(exp[i].equals("/")){ BigDecimal b2 = new BigDecimal(stack.pop()); BigDecimal b1 = new BigDecimal(stack.pop()); BigDecimal b3 = new BigDecimal(0); double d1 = b1.doubleValue(); double d2 = b2.doubleValue(); if(d1%d2 == 0){ b3 = (b1.divide(b2)); stack.push(b3.toString()); }else { b3 = b1.divide(b2,10, RoundingMode.HALF_UP); stack.push(b3.toString()); } } } Res = stack.pop(); boolean flag = false; for (int m = 0; m < Res.length() - 1;m++) { if(Res.charAt(m) == '.'){ flag = true; } } if(flag) { for(int m = Res.length()-1;m >= 0;m--) { if(Res.charAt(m) == '0'){ }else { Res = Res.substring(0,m+1); break; } } if(Res.charAt(Res.length()-1) == '.') { Res = Res.substring(0,Res.length()-1); } } return Res; }總結(jié)
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