Lambda Demos

Motivation

JDK 8 added lambdas to alleviate the bulkiness of anonymous inner classes. We use lambdas heavily in 231.

Background

Lambda Expressions

Code To Investigate

fork join

System.out.println("start");

Future<Void> apples = void_fork(() -> {
	sleepRandom(1_000);
	System.out.println("-apples");
});
Future<Void> oranges = void_fork(() -> {
	sleepRandom(1_000);
	System.out.println("--oranges");
});
Future<Void> bananas = void_fork(() -> {
	sleepRandom(1_000);
	System.out.println("---bananas");
});
Future<Void> mangoes = void_fork(() -> {
	sleepRandom(1_000);
	System.out.println("----mangoes");
});

join(apples, oranges, bananas, mangoes);

System.out.println("stop");

class:	LambdasForkJoinExample.java	DEMO:
methods:	main
package:	lambda.forkjoin.demo
source folder:	src/demo/java

class:	AnonymousInnerClassesForkJoinExample.java	DEMO:
methods:	main
package:	lambda.forkjoin.demo
source folder:	src/demo/java

class:	NamedClassesForkJoinExample.java	DEMO:
methods:	main
package:	lambda.forkjoin.demo
source folder:	src/demo/java

fork join

X10 x10 = new ForkJoinX10();
System.out.println("start");

x10.void_finish(() -> {
	void_fork(() -> {
		sleepRandom(1_000);
		System.out.println("-apples");
	});
	void_fork(() -> {
		sleepRandom(1_000);
		System.out.println("--oranges");
	});
	void_fork(() -> {
		sleepRandom(1_000);
		System.out.println("---bananas");
	});
	void_fork(() -> {
		sleepRandom(1_000);
		System.out.println("----mangoes");
	});
});

System.out.println("stop");

class:	LambdasFinishExample.java	DEMO:
methods:	main
package:	lambda.x10.demo
source folder:	src/demo/java

class:	AnonymousInnerClassesFinishExample.java	DEMO:
methods:	main
package:	lambda.x10.demo
source folder:	src/demo/java

class:	NamedClassesFinishExample.java	DEMO:
methods:	main
package:	lambda.x10.demo
source folder:	src/demo/java

compute

String text = "abracadabra";
// NOTE: we use a TreeMap<K,V> since it is sorted producing consistent output
Map<Character, Integer> mapCharacterToCount = new TreeMap<>();
for( char ch : text.toCharArray() ) {
	// https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#compute-K-java.util.function.BiFunction-
	mapCharacterToCount.compute(ch, (Character character, Integer count)-> {
		if( count != null ) {
			//we have associated character before
			return count+1;
		} else {
			//first encounter with character
			return 1;
		}
	});
}
for( Entry<Character, Integer> entry : mapCharacterToCount.entrySet() ) {
	System.out.println(entry);
}

class:	LambdasMapComputeExample.java	DEMO:
methods:	demo
package:	lambda.demo.compute
source folder:	src//java

class:	AnonymousInnerClassesMapComputeExample.java	DEMO:
methods:	demo
package:	lambda.demo.compute
source folder:	src//java

class:	NamedClassesMapComputeExample.java	DEMO:
methods:	demo
package:	lambda.demo.compute
source folder:	src//java

user interface

buttonI.addActionListener((ActionEvent e) -> {
	System.out.println(">>> entering lambda");
	System.out.println("    " + accessible_within_lambda_i
			+ "            (note: runtime stack with local variable i long since popped)");
	System.out.println("<<< leaving  lambda");
	System.out.println();
	// Thread.dumpStack();
});

class:	LambdaDemoApp.java	VIZ
package:	lambda.demo.viz
source folder:	student/src/demo/java