我可以运行此代码，只需将其打印到控制台，然后一切都可以正常打印，然后将所有System.out.println更改为outputStream.write （“某些字符串”）根本不会写入输出文件。它只是空白。第一个文件是主文件。然后我的其他类是MyStack和PostfixError。我将把它们包括在此之下。该代码从在命令行中输入的输入文件中获取输入，然后将其输出到也由命令行指定的文件中。输入文件应采用Postfix格式，例如ABC +-或AB + C。如果不是这种格式，则会产生错误。如果输入采用的是这种格式，那么代码将采用该输入，并编写指令（如果我们使用的是只有一个寄存器的计算机，则需要使用该指令来评估后缀表达式）。
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.FileWriter;
public class PostfixEvaluation{
public static void main(String[] args) throws PostfixError, IOException{
FileReader inputStream = null;
FileReader inputStream2 = null;
FileWriter outputStream = null;
BufferedReader str = null;
int c, j=1,letter;
int stringSize = 100;
String message, letterA, letterB;
try {
inputStream = new FileReader(args[0]); // input file
inputStream2 = new FileReader(args[0]);
outputStream = new FileWriter(args[1]); // output file
str = new BufferedReader(inputStream);
String nextLine; //= str.readLine();
while ((nextLine = str.readLine()) != null) {
outputStream.write("");
outputStream.write("Current expression being evaluated is " + nextLine);
MyStack letterStack = new MyStack(stringSize);
try {
while ((c = inputStream2.read()) != 10){
//letterStack = EvaluateInstructions(c, letterStack,j);
letter = c;
if (letter == 65){ // use an or to account for lower case letters
letterStack.push("A");
}else if (letter == 66) {
letterStack.push("B");
}else if (letter == 67) {
letterStack.push("C");
}else if (letter == 68) {
letterStack.push("D");
}else if (letter == 69) {
letterStack.push("E");
}else if (letter == 70) {
letterStack.push("F");
}else if (letter == 71) {
letterStack.push("G");
}else if (letter == 72) {
letterStack.push("H");
}else if (letter == 73) {
letterStack.push("I");
}else if (letter == 74) {
letterStack.push("J");
}else if (letter == 75) {
letterStack.push("K");
}else if (letter == 76) {
letterStack.push("L");
}else if (letter == 77) {
letterStack.push("M");
}else if (letter == 78) {
letterStack.push("N");
}else if (letter == 79) {
letterStack.push("O");
}else if (letter == 80) {
letterStack.push("P");
}else if (letter == 81) {
letterStack.push("Q");
}else if (letter == 82) {
letterStack.push("R");
}else if ( letter == 83) {
letterStack.push("S");
}else if (letter == 84) {
letterStack.push("T");
}else if (letter == 85) {
letterStack.push("U");
}else if (letter == 86) {
letterStack.push("V");
}else if (letter == 87) {
letterStack.push("W");
}else if (letter == 88){
letterStack.push("X");
}else if (letter == 89) {
letterStack.push("Y");
}else if (letter == 90) {
letterStack.push("Z");
}else if (letter == 42){ //letter == '*'
if (letterStack.isEmpty()|letterStack.length() <= 1) {
j=1;
throw new PostfixError("There are more operators than operands; This is not a valid expression.");
}else {
letterA = letterStack.pop();
letterB = letterStack.pop();
outputStream.write("LD " + letterB);
outputStream.write("ML " + letterA);
outputStream.write("ST TEMP"+j);
letterStack.push("TEMP"+j);
//throw new PrintToOutput("hello");
//j++;
}
}else if (letter == 47) { //letter == '/'
if (letterStack.isEmpty()|letterStack.length() <= 1) {
j=1;
throw new PostfixError("There are more operators than operands; This is not a valid expression.");
}else {
letterA = letterStack.pop();
letterB = letterStack.pop();
outputStream.write("LD " + letterB);
outputStream.write("DV " + letterA);
outputStream.write("ST TEMP"+j);
letterStack.push("TEMP"+j);
//j++;
}
}else if (letter == 43) { //letter == '+'
if (letterStack.isEmpty()|letterStack.length() <= 1) {
j=1;
throw new PostfixError("There are more operators than operands; This is not a valid expression.");
}else {
letterA = letterStack.pop();
letterB = letterStack.pop();
outputStream.write("LD " + letterB);
outputStream.write("AD " + letterA);
outputStream.write("ST TEMP"+j);
letterStack.push("TEMP"+j);
//j++;
}
}else if (letter == 45) { //letter == '-'
if (letterStack.isEmpty()|letterStack.length() <= 1) {
j=1;
throw new PostfixError("There are more operators than operands. This is not a valid expression.");
}else {
letterA = letterStack.pop();
letterB = letterStack.pop();
outputStream.write("LD " + letterB);
outputStream.write("SB " + letterA);
outputStream.write("ST TEMP"+j);
letterStack.push("TEMP"+j);
//j++;
}
}else if (letter == 13) {
//do nothing
}else if (letter == -1) {
outputStream.write("");
outputStream.write("Success! File is finished being read.");
System.exit(0);
}else {
j=1;
//need to empty stack
throw new PostfixError( "This input has an incorrect character or combination of characters.");
}
if (c == 47 | c == 42 | c == 45 |c == 43) {
j++;
}else if (c == 13) {
j=1;
}
}
}catch (PostfixError e) {
outputStream.write(e.getMessage());
//read input stream until it equals 10
do {
c=inputStream2.read();
}while (c !=10);
}
}
} finally {
if (inputStream != null) inputStream.close();
if (inputStream2 !=null) inputStream2.close();
if (outputStream != null) outputStream.close();
str.close();
}
}
}
MyStack类
public class MyStack {
private String[] theStack;
private int size;
private int top;
private int totalLength;
public MyStack() {
size = 100;
theStack = new String[size];
top = -1;
}
public MyStack(int stringSize) {
size = 100;
theStack = new String[stringSize];
top = 0;
}
public void push(String symbol) {
theStack[top] = symbol;
top++;
}
public String pop() {
return theStack[--top];
}
public boolean isEmpty() {
if (top == -1) {
return true;
}else {
return false;
}
}
public int length() {
return totalLength = top;
}
public void print() {
for(int i=0;i<=top;i++){
System.out.print(theStack[i]+ " ");
}
System.out.println();
}
}
PostfixError类
public class PostfixError extends Exception{
public PostfixError(String message) {
super(message);
}
}
答案 0 :(得分：0)
您致电System.exit；这立即退出；您的“最终”代码块未运行。结果，您的BufferedWriter被遗弃了； flush()和close()都不会被调用，这意味着它不会将其缓冲区刷新到文件中。
解决方案：请勿在此处调用System.exit。