Applied Refactoring techniques to improve code quality

[damank16]

Please review my pull request and if you find it useful then please accept it. it is very important for me if you could do it on or before 27 March, 2022. Thanks in advance.

Description:

1. Refactoring name: EXTRACT METHOD
   Location: src/main/java/simpledb/algorithm/Join
   • File: src/main/java/simpledb/algorithm/Join/SortMergeJoin.java
   • Class: SortMergeJoin.java
   • Method: mergeJoin

To reduce duplicate code and cyclomatic complexity: Extracted code block from mergeJoin() and created two new methods
a)joinTuples() which joins the tuple based on predicate operator(LESS_THAN_OR_EQ or GREATER_THAN_OR_EQ) passed.
b)equalsPredicate.

2. Refactoring name: RENAME VARIABLE
   Location: src/main/java/simpledb/index
   • File: src/main/java/simpledb/index/BTreeFile.java
   • Class: BTreeFile.java
   Class level field is renamed from f to file for better understanding and readability.

3. Refactoring name: PULL UP VARIABLE
   Location: src/main/java/simpledb/execution
   • File: src/main/java/simpledb/execution/Operator.java
   • Class: Operator.java
   • Variable: TupleDesc td;

Location: src/main/java/simpledb/execution
• File: src/main/java/simpledb/execution/Aggregate.java
• Class: Aggregate.java

Location: src/main/java/simpledb/execution
• File: src/main/java/simpledb/execution/Delete.java
• Class: Delete.java

Location: src/main/java/simpledb/execution
• File: src/main/java/simpledb/execution/Filter.java
• Class: Filter.java

Location: src/main/java/simpledb/execution
• File: src/main/java/simpledb/execution/HashEquiJoin.java
• Class: HashEquiJoin.java

Location: src/main/java/simpledb/execution
• File: src/main/java/simpledb/execution/Insert.java
• Class: Insert.java

Location: src/main/java/simpledb/execution
• File: src/main/java/simpledb/execution/Join.java
• Class: Join.java

Location: src/main/java/simpledb/execution
• File: src/main/java/simpledb/execution/OrderBy.java
• Class: OrderBy.java

Location: src/main/java/simpledb/execution
• File: src/main/java/simpledb/execution/Project.java
• Class: Project.java

To remove duplication of code for the variable of type TupleDesc in 8 classes,Pull up variable refactoring is performed and variable is pulled from 8 classes and is kept in the parent class Operator.

4 . Refactoring name: PUSH DOWN METHOD
Location: src/main/java/simpledb/algorithm/Join
• File: src/main/java/simpledb/algorithm/Join/JoinStrategy.java
• Class: JoinStrategy.java
• Method: close()

Location: src/main/java/simpledb/algorithm/Join
• File: src/main/java/simpledb/algorithm/Join/HashJoin.java
• Class: HashJoin.java
• Method: close()

Location: src/main/java/simpledb/algorithm/Join
• File: src/main/java/simpledb/algorithm/Join/NestedLoopJoin.java
• Class: NestedLoopJoin.java
• Method: close()

Location: src/main/java/simpledb/algorithm/Join
• File: src/main/java/simpledb/algorithm/Join/SortMergeJoin.java
• Class: SortMergeJoin.java
• Method: close()

close() method declared in JoinStrategy was being used in only one child class i.e SortMergeJoin and was not useful in other classes.It was defined with empty body in rest 2 classes.
Hence, close() method is moved to subclass SortMergeJoin and removed form parent class i.e Join/JoinStrategy.

5. Refactoring name: Change bidirectional association to unidirectional association
   Location: src/main/java/simpledb/optimizer
   • File: src/main/java/simpledb/optimizer/JoinOptimizer.java
   • Class: JoinOptimizer.java

Location: src/main/java/simpledb/optimizer/LogicalPlan.javaa
• File: src/main/java/simpledb/optimizer
• Class: LogicalPlan.java

Removed bidirectional asociation between JoinOptimizer and LogicalPlan classes. It reduces depenedency between these two classes since independent classes are easier to maintain.

Please let me know, in case of any queries.