docs: adding subject and main

subjects/java/checkpoints/builder-blueprint/ExerciseRunner.java

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+public class ExerciseRunner {
+    public static void main(String[] args) {
+        RegexDirector director = new RegexDirector();
+        RegexBuilder builder = new ConcreteRegexBuilder();
+        
+        director.setBuilder(builder);
+        Regex regex = director.construct();
+        
+        System.out.println(regex);
+    }
+}

subjects/java/checkpoints/builder-blueprint/README.md

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+## Builder Blueprint
+
+### Instructions
+
+You are given an incomplete Builder design pattern implementation with some incorrect parts. Complete and fix the classes to demonstrate your understanding of how the Builder design pattern works.
+
+Regex component required:
+- Any Character: `.`
+- Digit: `\d`
+- Whitespace : `\s`
+- Word Character: `\w`
+
+
+### Expected Classes
+
+```java
+// Regex class
+public class Regex {
+    private StringBuilder pattern;
+
+    public Regex(List<String> component) {
+       ...
+    }
+
+    public String getPattern() {
+        return pattern.toString();
+    }
+}
+
+// Builder interface
+public ... RegexBuilder {
+    void buildLiteral(String literal);
+    void buildAnyCharacter();
+    void buildDigit();
+    void buildWhitespace();
+    void buildWordCharacter();
+    Regex getResult();
+}
+
+// ConcreteRegexBuilder class
+public class ConcreteRegexBuilder {
+    private Regex regex = new Regex();
+    List<String> component;
+
+    ...
+
+    @Override
+    public Regex getResult() {
+        // Missing return statement
+    }
+}
+
+// RegexDirector class
+public class RegexDirector {
+    private RegexBuilder builder;
+
+    public void setBuilder(RegexBuilder builder) {
+        this.builder = builder;
+    }
+
+    public Regex construct() {
+        builder.buildLiteral("Hello");
+        builder.buildWhitespace();
+        builder.buildWordCharacter();
+        builder.buildAnyCharacter();
+        return builder.getResult();
+    }
+}
+```
+
+### Usage
+
+Here is a possible `ExerciseRunner.java` to test your classes:
+
+```java
+public class ExerciseRunner {
+    public static void main(String[] args) {
+        RegexDirector director = new RegexDirector();
+        RegexBuilder builder = new ConcreteRegexBuilder();
+        
+        director.setBuilder(builder);
+        Regex regex = director.construct();
+        
+        System.out.println(regex);
+    }
+}
+```
+
+### Expected Output
+
+```shell
+$ javac *.java -d build
+$ java -cp build ExerciseRunner
+Hello\s\w.
+$
+```