Lecture Notes: Enhanced For Loops in Java

Introduction to Enhanced For Loops

• Enhanced for loops, also known as for each loops, simplify iteration through items in a collection.
• Commonly used with arrays, but applicable to various collections.

Key Questions When Using Enhanced For Loops

1. Name of the Collection: Identify the array or collection to iterate through.
2. Type of Elements: Determine the data type of individual elements in the collection.

Example: Iterating Over a Double Array

• Array Example: Double array named interestRates containing four doubles.
• Objective: Print all items using an enhanced for loop.
• Memory Representation:
  • interestRates points to a memory address storing the doubles.
  • Direct printing of interestRates yields a memory address, not values.

Steps to Create an Enhanced For Loop

1. Start with the keyword for.
2. Right Side: Place the collection name (e.g., interestRates) on the right of the colon.
3. Left Side: Specify the type of elements (e.g., double) and declare a temporary variable (e.g., rate).
4. Inside Loop: Use System.out.println(rate) to print each element.

Execution

• Iterates through interestRates, printing each rate (2.9, 3.5, 4.8, 6.7) sequentially.

Example: Iterating Over a String Array

• Array Example: String array named colors with rainbow colors.
• Objective: Print each color to the console.
• Loop Setup:
  • Use colors on the right, String and currentColor on the left.
  • Print using System.out.println(currentColor).

String Operations

• Can perform string operations within the loop, such as currentColor.charAt(0) to print the first character of each color.

When to Use Enhanced For Loops

• Ideal for retrieving values:
  • Printing elements.
  • Searching collections (e.g., finding max/min values).
• Not suitable for updating values or operations requiring indices.

Example: Incorrect Usage of Enhanced For Loop

• Objective: Attempting to update values by increasing each rate by 0.2.
• Issue: rate = rate + 0.03 does not update the interestRates array.
  • Changes affect only the temporary variable (rate), not the original array.
• Memory Explanation:
  • Primitive types are separate in memory, so changes do not affect the original collection.

Caution and Conclusion

• Enhanced for loops are beneficial for retrieving but not modifying values.
• Primitive Types vs. Reference Types:
  • Enhanced for loops behave differently with reference types (not covered in this lecture).

Final Note

• Enhanced for loops streamline iteration but require careful use to avoid unintended outcomes when updating elements.
• Understanding memory interaction is key to effectively using enhanced for loops.