Implement FindEmailCommand class

src/main/java/seedu/address/logic/commands/AbstractFindCommand.java

@@ -20,7 +20,7 @@ public abstract class AbstractFindCommand extends Command {
             + "Parameters: KEYWORD [MORE_KEYWORDS]...\n"
             + "Example: " + COMMAND_WORD + " alice bob charlie";
 
-    private final ContainsKeywordsPredicate predicate;
+    protected final ContainsKeywordsPredicate predicate;
 
     public AbstractFindCommand(ContainsKeywordsPredicate predicate) {
         this.predicate = predicate;

src/main/java/seedu/address/logic/commands/FindEmailCommand.java

@@ -0,0 +1,30 @@
+package seedu.address.logic.commands;
+
+import seedu.address.model.person.EmailContainsKeywordsPredicate;
+
+public class FindEmailCommand extends AbstractFindCommand {
+
+    public static final String COMMAND_WORD = "find /e";
+
+    public static final String MESSAGE_USAGE = COMMAND_WORD + ": Finds all persons whose emails "
+            + "contain any of the specified keywords (case-insensitive) and displays them as a list with indices.\n"
+            + "Parameters: KEYWORD [MORE_KEYWORDS]...\n"
+            + "Example: " + COMMAND_WORD + " alice bob charlie";
+
+    public FindEmailCommand(EmailContainsKeywordsPredicate predicate) {
+        super(predicate);
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        if (other == this) {
+            return true;
+        }
+
+        // instanceof handles nulls
+        if (!(other instanceof FindEmailCommand otherFindCommand)) {
+            return false;
+        }
+        return super.predicate.equals(otherFindCommand.predicate);
+    }
+}

src/main/java/seedu/address/model/person/EmailContainsKeywordsPredicate.java

@@ -14,6 +14,7 @@ public EmailContainsKeywordsPredicate(List<String> keywords) {
         super(keywords);
     }
 
+    // checks if the person contains the keyword
     @Override
     public boolean test(Person person) {
         return super.getKeywords().stream()
@@ -27,11 +28,10 @@ public boolean equals(Object other) {
         }
 
         // instanceof handles nulls
-        if (!(other instanceof EmailContainsKeywordsPredicate)) {
+        if (!(other instanceof EmailContainsKeywordsPredicate otherNameContainsKeywordsPredicate)) {
             return false;
         }
 
-        EmailContainsKeywordsPredicate otherNameContainsKeywordsPredicate = (EmailContainsKeywordsPredicate) other;
         return this.getKeywords().equals(otherNameContainsKeywordsPredicate.getKeywords());
     }
 

src/main/java/seedu/address/model/person/Person.java

@@ -85,11 +85,10 @@ public boolean equals(Object other) {
         }
 
         // instanceof handles nulls
-        if (!(other instanceof Person)) {
+        if (!(other instanceof Person otherPerson)) {
             return false;
         }
 
-        Person otherPerson = (Person) other;
         return name.equals(otherPerson.name)
                 && phone.equals(otherPerson.phone)
                 && email.equals(otherPerson.email)