Java 8 Stream API Lecture Notes

Introduction to Stream API

• Purpose: Stream API is used to process collections of objects, enabling operations such as filtering, mapping, and reducing.
• Definition: A stream is a sequence of objects that supports various methods that can be pipelined to produce a desired result.
• Characteristics:
  • Not a data structure.
  • Takes input from collections or arrays.
  • Does not modify the original data structure but provides results based on pipeline methods.

Advantages of Stream API

• Functional Programming: Supports lambda expressions, representing functional interfaces.
• Code Reduction: Reduces code length by using lambda expressions and method chaining.
• Bulk Operations: Suitable for operations on large data collections, offering better performance compared to traditional approaches.

Key Methods in Stream API

1. forEach

• Purpose: Used for iterating over elements.
• Implementation:
  • Convert collection to a stream.
  • Use forEach to iterate, with a lambda expression representing a Consumer.
  • Example: list.stream().forEach(System.out::println);

2. filter

• Purpose: Used for conditional checks, similar to if-else.
• Implementation:
  • Convert collection to a stream.
  • Use filter with a predicate to specify conditions.
  • Example: list.stream().filter(s -> s.startsWith("M")).forEach(System.out::println);

Using forEach and filter with Collections

Lists

• Iteration: Traditional iteration vs. using forEach in streams.
• Filtering: Using filter to select elements that meet a condition.

Maps

• Iteration: Directly iterate using forEach or convert entry set to a stream for advanced operations.
• Filtering: Use filter to apply conditions to map entries.

Internal Working of forEach

• Consumer Interface: forEach uses Consumer's accept method.
• Lambda Expression: Simplifies iteration by replacing method definitions with expressions.

Internal Working of filter

• Predicate Interface: filter uses Predicate's test method.
• Condition: Only elements that satisfy the predicate condition are included in the result.

Real-World Example

• Scenario: Determine employees eligible for tax based on salary.
• Implementation:
  • Create a list of employees.
  • Use stream() and filter to separate taxable and non-taxable employees based on salary condition.
  • Use ternary operators to simplify if-else logic.
• Outcome: Efficiently process employee data using streams.

Conclusion

• Stream API significantly simplifies handling collections with concise and functional-style code.
• Key methods like forEach and filter are crucial for iterating and applying conditions on collections.