Interpreter Pattern - The main cause of Y2K issue was date format, in this exmaple we made an interpreter which can intrepret any date format

Author: premaseem

InterpreterPattern/.gitignore

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+/bin

InterpreterPattern/src/com/premaseem/interpreterPattern/AbstractExpression.java

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+package com.premaseem.interpreterPattern;
+
+import java.util.Date;
+
+public abstract class AbstractExpression {
+
+	public abstract void evaluate(Context context);
+}
+
+class DayExpression extends AbstractExpression
+{
+
+  @Override
+  public void evaluate( Context context )
+  {
+    String expression = context.getExpression();
+    Date date = context.getDate();
+    Integer day = new Integer(date.getDate());
+    String tempExpression = expression.replaceAll("DD", day.toString());
+    context.setExpression(tempExpression);
+  }
+}
+
+class MonthExpression extends AbstractExpression
+{
+
+  @Override
+  public void evaluate( Context context )
+  {
+    String expression = context.getExpression();
+    Date date = context.getDate();
+    Integer month = new Integer(date.getMonth()+1);
+    String tempExpression = expression.replaceAll("MM", month.toString());
+    context.setExpression(tempExpression);
+  }
+
+}
+
+class YearExpression extends AbstractExpression
+{
+
+  @Override
+  public void evaluate( Context context )
+  {
+    String expression = context.getExpression();
+    Date date = context.getDate();
+    Integer year = new Integer(date.getYear() + 1900);
+    String tempExpression = expression.replaceAll("YYYY", year.toString());
+    context.setExpression(tempExpression);
+  }
+
+}

InterpreterPattern/src/com/premaseem/interpreterPattern/ClientFile.java

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+package com.premaseem.interpreterPattern;
+
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.Scanner;
+
+public class ClientFile {
+
+	public static void main(String[] args) {
+
+		System.out.println("Welcome to Interpreter Design pattern which interpretes your date format accross all languages ");
+		Scanner scan = new Scanner(System.in);
+
+		// Object initialization block
+
+		// User input block
+		String repeatRunFlag = "yes";
+		while (!repeatRunFlag.equalsIgnoreCase("no")) {
+
+		System.out.println("Please select the Expression  : 'MM-DD-YYYY' or 'YYYY-MM-DD'");
+		Scanner scanner = new Scanner(System.in);
+		String expression = scanner.next();
+
+		Context context = new Context();
+		context.setExpression(expression);
+		context.setDate(new Date());
+
+		ArrayList<AbstractExpression> expressionOrderList = getExpressionOrder(context);
+
+		System.out.println("Input : " + context.getExpression() + " : " + new Date());
+
+		for (AbstractExpression abstractExpression : expressionOrderList) {
+			abstractExpression.evaluate(context);
+			System.out.println(abstractExpression.getClass().getSimpleName() + " Evaluated     : " + context.getExpression());
+
+		}
+
+		System.out.println("Output : " + context.getExpression());
+		
+		System.out.println("Press No to Exit and any other character to repeat  .... ");
+		try {
+			repeatRunFlag = scan.next();
+		} catch (Exception e) {
+			repeatRunFlag = "no";
+		}
+
+	}
+
+	System.out.println("\n $$$$$$$$$$$$$$$$$$$$  Thanks by Prem Aseem $$$$$$$$$$$$$$$$$$$$$$ \n ");
+	System.out.println("\n $$$$$$$$$$$$$$$$$$$$$  www.premaseem.com  $$$$$$$$$$$$$$$$$$$$$$ \n ");
+	}
+
+	private static ArrayList<AbstractExpression> getExpressionOrder(Context context) {
+		ArrayList<AbstractExpression> expressionOrderList = new ArrayList<AbstractExpression>();
+		String[] strArray = context.getExpression().split("-");
+		for (String string : strArray) {
+			if (string.equalsIgnoreCase("MM")) {
+				expressionOrderList.add(new MonthExpression());
+			} else if (string.equalsIgnoreCase("DD")) {
+				expressionOrderList.add(new DayExpression());
+			} else {
+				expressionOrderList.add(new YearExpression());
+			}
+
+		}
+		return expressionOrderList;
+	}
+}

InterpreterPattern/src/com/premaseem/interpreterPattern/Context.java

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+package com.premaseem.interpreterPattern;
+
+import java.util.Date;
+
+public class Context {
+	public String expression;
+	public Date date;
+
+	public String getExpression() {
+		return expression;
+	}
+
+	public void setExpression(String expression) {
+		this.expression = expression;
+	}
+
+	public Date getDate() {
+		return date;
+	}
+
+	public void setDate(Date date) {
+		this.date = date;
+	}
+
+}