BYR Achieve · 镜像论坛

这是一个RPN计算器。输入“1 2 + 3 *”，得到9. 每个组件传入参数，返回结果。但是main函数麻烦。 package rpn.returning; import java.util.*; import java.io.*; class Reader { public String read(InputStream is) throws IOException { Scanner s = new Scanner(is); return s.nextLine(); } } class Lexer { public String[] lex(String expression) { return expression.split(" +"); } } class Evaluator { public int eval(String[] tokens) { Stack<Integer> stack = new Stack<Integer>(); for (String token : tokens) { try { int num = Integer.parseInt(token); stack.push(num); } catch (NumberFormatException e) { int num2 = stack.pop(); int num1 = stack.pop(); int result; if (token.equals("+")) { result = num1 + num2; } else if (token.equals("-")) { result = num1 - num2; } else if (token.equals("*")) { result = num1 * num2; } else if (token.equals("/")) { result = num1 / num2; } else { throw new IllegalArgumentException("Illegal expression"); } stack.push(result); } } return stack.pop(); } } class Printer { void print(int result, PrintStream out) { out.println(result); } } public class RPNReturningDemo { public static void main(String[] args) throws IOException { Reader reader = new Reader(); Lexer lexer = new Lexer(); Evaluator evaluator = new Evaluator(); Printer printer = new Printer(); while(true) { String expression = reader.read(System.in); String[] tokens = lexer.lex(expression); int result = evaluator.eval(tokens); printer.print(result, System.out); } } } 下面这个程序是同样的功能。每个组件把结果推给下一个组件。但是组件之间互相依赖。 package rpn.pushing; import java.util.*; import java.io.*; class Reader { interface ResultHandler { void handle(String line); } private ResultHandler resultHandler; public ResultHandler getResultHandler() { return resultHandler; } public void setResultHandler(ResultHandler resultHandler) { this.resultHandler = resultHandler; } public void read(InputStream is) throws IOException { Scanner s = new Scanner(is); String line = s.nextLine(); resultHandler.handle(line); } } class Lexer implements Reader.ResultHandler { interface ResultHandler { void handle(String[] tokens); } private ResultHandler resultHandler; public ResultHandler getResultHandler() { return resultHandler; } public void setResultHandler(ResultHandler resultHandler) { this.resultHandler = resultHandler; } public String[] lex(String expression) { return expression.split(" +"); } @Override public void handle(String line) { String[] tokens = lex(line); resultHandler.handle(tokens); } } class Evaluator implements Lexer.ResultHandler { interface ResultHandler { void handle(int result); } private ResultHandler resultHandler; public ResultHandler getResultHandler() { return resultHandler; } public void setResultHandler(ResultHandler resultHandler) { this.resultHandler = resultHandler; } public int eval(String[] tokens) { Stack<Integer> stack = new Stack<Integer>(); for (String token : tokens) { try { int num = Integer.parseInt(token); stack.push(num); } catch (NumberFormatException e) { int num2 = stack.pop(); int num1 = stack.pop(); int result; if (token.equals("+")) { result = num1 + num2; } else if (token.equals("-")) { result = num1 - num2; } else if (token.equals("*")) { result = num1 * num2; } else if (token.equals("/")) { result = num1 / num2; } else { throw new IllegalArgumentException("Illegal expression"); } stack.push(result); } } return stack.pop(); } @Override public void handle(String[] tokens) { int result = eval(tokens); resultHandler.handle(result); } } class Printer implements Evaluator.ResultHandler { private PrintStream printStream; public PrintStream getPrintStream() { return printStream; } public void setPrintStream(PrintStream printStream) { this.printStream = printStream; } void print(int result) { printStream.println(result); } @Override public void handle(int result) { print(result); } } public class RPNPushingDemo { public static void main(String[] args) throws IOException { Reader reader = new Reader(); Lexer lexer = new Lexer(); Evaluator evaluator = new Evaluator(); Printer printer = new Printer(); reader.setResultHandler(lexer); lexer.setResultHandler(evaluator); evaluator.setResultHandler(printer); printer.setPrintStream(System.out); while (true) { reader.read(System.in); } } } 为了避免互相依赖，组件不再实现上游的接口，在主函数中创建连接器。 package rpn.pushing2; import java.util.*; import java.io.*; class Reader { interface ResultHandler { void handle(String line); } private ResultHandler resultHandler; public ResultHandler getResultHandler() { return resultHandler; } public void setResultHandler(ResultHandler resultHandler) { this.resultHandler = resultHandler; } public void read(InputStream is) throws IOException { Scanner s = new Scanner(is); String line = s.nextLine(); resultHandler.handle(line); } } class Lexer { interface ResultHandler { void handle(String[] tokens); } private ResultHandler resultHandler; public ResultHandler getResultHandler() { return resultHandler; } public void setResultHandler(ResultHandler resultHandler) { this.resultHandler = resultHandler; } public String[] lex(String expression) { return expression.split(" +"); } } class Evaluator { interface ResultHandler { void handle(int result); } private ResultHandler resultHandler; public ResultHandler getResultHandler() { return resultHandler; } public void setResultHandler(ResultHandler resultHandler) { this.resultHandler = resultHandler; } public int eval(String[] tokens) { Stack<Integer> stack = new Stack<Integer>(); for (String token : tokens) { try { int num = Integer.parseInt(token); stack.push(num); } catch (NumberFormatException e) { int num2 = stack.pop(); int num1 = stack.pop(); int result; if (token.equals("+")) { result = num1 + num2; } else if (token.equals("-")) { result = num1 - num2; } else if (token.equals("*")) { result = num1 * num2; } else if (token.equals("/")) { result = num1 / num2; } else { throw new IllegalArgumentException("Illegal expression"); } stack.push(result); } } return stack.pop(); } } class Printer { private PrintStream printStream; public PrintStream getPrintStream() { return printStream; } public void setPrintStream(PrintStream printStream) { this.printStream = printStream; } void print(int result) { printStream.println(result); } } public class RPNPushing2Demo { public static void main(String[] args) throws IOException { final Reader reader = new Reader(); final Lexer lexer = new Lexer(); final Evaluator evaluator = new Evaluator(); final Printer printer = new Printer(); reader.setResultHandler(new Reader.ResultHandler() { @Override public void handle(String line) { lexer.lex(line); } }); lexer.setResultHandler(new Lexer.ResultHandler() { @Override public void handle(String[] tokens) { evaluator.eval(tokens); } }); evaluator.setResultHandler(new Evaluator.ResultHandler() { @Override public void handle(int result) { printer.print(result); } }); printer.setPrintStream(System.out); while (true) { reader.read(System.in); } } } 下面这个程序功能还是一样的，每个组件从上游获取数据。当然，连接器在main中创建，组件不互相依赖。 package rpn.pulling; import java.util.*; import java.io.*; class Reader { private InputStream inputStream; private Scanner scanner; public void setInputStream(InputStream inputStream) { this.inputStream = inputStream; this.scanner = new Scanner(inputStream); } public String read() throws IOException { return scanner.nextLine(); } } class Lexer { public interface Source { String get(); } private Source source; public void setSource(Source source) { this.source = source; } public String[] lex() { return source.get().split(" +"); } } class Evaluator { public interface Source { String[] get(); } private Source source; public void setSource(Source source) { this.source = source; } public int eval() { String[] tokens = source.get(); Stack<Integer> stack = new Stack<Integer>(); for (String token : tokens) { try { int num = Integer.parseInt(token); stack.push(num); } catch (NumberFormatException e) { int num2 = stack.pop(); int num1 = stack.pop(); int result; if (token.equals("+")) { result = num1 + num2; } else if (token.equals("-")) { result = num1 - num2; } else if (token.equals("*")) { result = num1 * num2; } else if (token.equals("/")) { result = num1 / num2; } else { throw new IllegalArgumentException("Illegal expression"); } stack.push(result); } } return stack.pop(); } } class Printer { public interface Source { int get(); } private Source source; public void setSource(Source source) { this.source = source; } void print(PrintStream out) { out.println(source.get()); } } public class RPNPullingDemo { public static void main(String[] args) throws IOException { final Reader reader = new Reader(); final Lexer lexer = new Lexer(); final Evaluator evaluator = new Evaluator(); final Printer printer = new Printer(); reader.setInputStream(System.in); lexer.setSource(new Lexer.Source() { @Override public String get() { try { return reader.read(); } catch (IOException e) { e.printStackTrace(); throw new Error("Cannot throw since the interface cannot be changed.", e); } } }); evaluator.setSource(new Evaluator.Source() { @Override public String[] get() { return lexer.lex(); } }); printer.setSource(new Printer.Source() { @Override public int get() { return evaluator.eval(); } }); while (true) { printer.print(System.out); } } } 哪个比较好？有没有更好的？当然这是一个例子，实际程序会更复杂。反正我印象中，自己写的代码出现过以上好几种。也见过别人的API属于以上某一种或几种。

不怕脑残的进来