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Calculator/.classpath

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+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/J2SE-1.5"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>

Calculator/.project

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+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>Calculator</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>

Calculator/.settings/org.eclipse.jdt.core.prefs

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+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.5
+org.eclipse.jdt.core.compiler.codegen.unusedLocal=preserve
+org.eclipse.jdt.core.compiler.compliance=1.5
+org.eclipse.jdt.core.compiler.debug.lineNumber=generate
+org.eclipse.jdt.core.compiler.debug.localVariable=generate
+org.eclipse.jdt.core.compiler.debug.sourceFile=generate
+org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
+org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.source=1.5

Calculator/src/calculator/Calculator.java

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+package calculator;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.Vector;
+
+/**
+ * 实现对字符串的计算
+ * 输入的是后缀表示
+ * ABCD-*+EF/-
+ * 中缀表达式为:
+ * A+B*(C-D)-E/F
+ * 这个程序没有进行错误控制
+ * 输入字符串时一定要按照标准输入
+ * 否则将会出现错误
+ * @author majinliang
+ *
+ */
+public class Calculator {
+
+	public StringBuffer  phrase;//存储当前正在形成的词,用于词法分析
+	public String str;//存储整个字符串，用于词法分析
+
+	public static void main(String[] args) {
+		Calculator c = new Calculator();
+		String str = null;
+		//从控制台读入一行字符串
+		//输入数字只允许整数
+		//因为词法分析时，只是对整数进行了考虑
+		try {
+			BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
+			str = stdin.readLine();
+		} catch (IOException e) {
+			e.printStackTrace();
+		}
+		Vector<String> v = c.phraseAnalysis(str);
+		/*for(int i = 0; i < v.size(); i++){
+			System.out.println(v.get(i));
+		}*/
+		c.run(v);
+	}
+
+	/*
+	 * 进行词法分析
+	 * 两个相邻的数字之间用空格隔开
+	 * 其他情况可以使用空格隔开，也可以不适用空格隔开
+	 */
+	public Vector<String> phraseAnalysis(String in){
+		Vector<String> phraseVector = new Vector<String>();
+		str = in;
+		int position = 0;
+		phrase = new StringBuffer();
+		char ch = str.charAt(position);
+		while(position < str.length()){
+			ch = str.charAt(position);
+			if(ch == '*'||ch == '-'||ch == '+'||ch == '/'){
+				phrase.append(ch);
+				position= position + 1;
+				if(position < str.length())
+					ch = str.charAt(position);
+				phraseVector.add(phrase.toString());
+				phrase.setLength(0);
+			}else{
+				if(ch >= '0' && ch <= '9'){	
+					while(ch>='0'&&ch<='9'){
+						ch = str.charAt(position);
+						phrase.append(ch);
+						position= position + 1;
+						ch = str.charAt(position);
+					}
+					phraseVector.add(phrase.toString());
+					phrase.setLength(0);
+				}else{
+					position= position + 1;
+
+				}
+			}		
+		}
+		return phraseVector;
+	}
+
+
+	/*
+	 * 判读一个字符串是否为数字
+	 */
+	boolean isNumber(String str){
+		int temp = 0; 
+		try{
+		    temp = Integer.parseInt(str);
+		}catch(Exception e){
+		    return false;
+		}
+		return true;
+	}
+
+
+	public void run(Vector<String> v){
+		Stack stack = new Stack(v.get(0));
+		for(int i = 1; i < v.size(); i++){
+			if(isNumber(v.get(i))){
+				stack.push(v.get(i));
+			}else{
+				if(v.get(i).equals("+")){
+					String str1 = stack.pop();
+					String str2 = stack.pop();
+					double jieguo = Double.parseDouble(str2) + Double.parseDouble(str1);
+					stack.push(String.valueOf(jieguo));
+				}
+				if(v.get(i).equals("-")){
+					String str1 = stack.pop();
+					String str2 = stack.pop();
+					double jieguo = Double.parseDouble(str2) - Double.parseDouble(str1);
+					stack.push(String.valueOf(jieguo));
+				}
+				if(v.get(i).equals("*")){
+					String str1 = stack.pop();
+					String str2 = stack.pop();
+					double jieguo = Double.parseDouble(str2) * Double.parseDouble(str1);
+					stack.push(String.valueOf(jieguo));
+				}
+				if(v.get(i).equals("/")){
+					String str1 = stack.pop();
+					String str2 = stack.pop();
+					double jieguo = Double.parseDouble(str2) / Double.parseDouble(str1);
+					stack.push(String.valueOf(jieguo));
+				}
+			}
+		}
+
+		System.out.println(stack.pop());
+	}
+
+}

Calculator/src/calculator/Stack.java

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+package calculator;
+/*
+ * 栈
+ */
+public class Stack {
+
+	/*
+	 * 栈中的节点
+	 */
+	private class StackNode{
+		private String data;
+		private StackNode next;
+
+		public StackNode(String d, StackNode n){
+			data = d;
+			next = n;
+		}
+	}
+
+	//开始栈的部分
+	private StackNode top;
+
+	public Stack(String d){
+		top = new StackNode(d, null);
+	}
+
+	public void push(String str){
+		StackNode node = new StackNode(str, top);
+		top = node;
+	}
+
+	public String pop(){
+		String str = top.data;
+		top = top.next;
+		return str;
+	}	
+}