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# Lambda Expressions

📗 Lambda expressions are often used to create anonymous functions without formally defining them. 
📗 (args ...) -> {body ...}, for example:
➩ () -> System.out.println("line");
➩ (x) -> System.out.println(x);
➩ (x) -> x * x;
➩ (x, y) -> x * y;
📗 java.util.function interfaces: Doc

# Void in, Void out Example

📗 public interface Runnable { public void run(); }
➩ Runnable r1 = () -> System.out.println("line");
➩ Runnable r1 = () -> System.out.println("line1"); System.out.println("line2");};

# 1 Value in, Void out Example

📗 public interface Consumer { public void consume(double val1); }
➩ Consumer c1 = (x) -> System.out.println(x);
➩ Consumer c2 = (x) -> {double z = x * x; System.out.println(z);};

# 1 Value in, Value out

📗 public interface Function { public double apply(double val1); }
➩ Function f1 = (y) -> y * y;
➩ Function f2 = (y) -> {double z = y * y; System.out.println(z); return z;};

# 2 Values in, Value out

📗 public interface BiFunction { public double apply(double va1, double val2); }
➩ BiFunction b1 = (x, y) -> x * y;
➩ BiFunction b2 = (x, y) -> {double z = x * y; System.out.println(z); return z;};



# Java Streams

📗 A Java Stream requires: Doc
➩ Data source.
➩ Chain of intermediate operations: input stream -> operation -> output stream, for example, filter(Predicate), map(Function), limit(int), skip(int).
➩ One terminal operation, for example, findFirst(), forEach(Consumer), count(), min(Comparator), max(Comparator).
📗 Test these out: Link.

# Java Streams Examples

📗 Print all even numbers in a list.
📗 Compute the sum of all odd numbers in a list.
📗 Print the words in upper case in a list.
📗 Print the words in the list that start with "a".
📗 Compute the factorial of a positive integer.
📗 Check if a positive integer is a prime number.
📗 Approximate the sum \(\displaystyle\sum_{i=1}^{\infty} \dfrac{1}{i^{2}} = \dfrac{\pi^{2}}{6}\).
📗 Approximate the continued fraction \(1 + \dfrac{1}{1 + \dfrac{1}{1 + \dfrac{1}{1 + \dfrac{1}{1 + ...}}}} = \dfrac{1 + \sqrt{5}}{2}\).
📗 Approximate the continued fraction \(2 + \dfrac{2}{1 + \dfrac{1}{\dfrac{1}{2} + \dfrac{1}{\dfrac{1}{3} + \dfrac{1}{...}}}} = \pi\).



📗 Notes and code adapted from the course taught by Professor Florian Heimerl and Ashley Samuelson.
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Last Updated: December 14, 2025 at 10:42 PM