What is the easiest/shortest way to convert a Java 8 Stream into an array? 10 s 10 The easiest method is to use the toArray(IntFunction<A[]> generator) method with an array constructor reference. This is suggested in the API documentation for the method. String[] stringArray = stringStream.toArray(String[]::new); What it does is find a method that takes … Read more
I want to translate a List of objects into a Map using Java 8’s streams and lambdas. This is how I would write it in Java 7 and below. private Map<String, Choice> nameMap(List<Choice> choices) { final Map<String, Choice> hashMap = new HashMap<>(); for (final Choice choice : choices) { hashMap.put(choice.getName(), choice); } return hashMap; } … Read more
I was exploring the Java 8 source and found this particular part of code very surprising: //defined in IntPipeline.java @Override public final OptionalInt reduce(IntBinaryOperator op) { return evaluate(ReduceOps.makeInt(op)); } @Override public final OptionalInt max() { return reduce(Math::max); //this is the gotcha line } //defined in Math.java public static int max(int a, int b) { return … Read more
Editors note: This question was asked in 2014, and the answers may be outdated. I want to do some programming with the latest JavaFX, which requires Java 8. I’m using IntelliJ 13 CE and Mac OS X 9 Mavericks. I ran Oracle’s Java 8 installer, and the files look like they ended up at /Library/Java/JavaVirtualMachines/jdk1.8.0_05.jdk … Read more
The better practice is to use for-each. Besides violating the Keep It Simple, Stupid principle, the new-fangled forEach() has at least the following deficiencies: Can’t use non-final variables. So, code like the following can’t be turned into a forEach lambda: Object prev = null; for(Object curr : list) { if( prev != null ) foo(prev, … Read more
Both map and flatMap can be applied to a Stream<T> and they both return a Stream<R>. The difference is that the map operation produces one output value for each input value, whereas the flatMap operation produces an arbitrary number (zero or more) values for each input value. This is reflected in the arguments to each … Read more
You can use the getClass() method to get the type of the object you are using: Object obj = null; obj = new ArrayList<String>(); System.out.println(obj.getClass()); obj = “dummy”; System.out.println(obj.getClass()); obj = 4; System.out.println(obj.getClass()); This will generate the following output: class java.util.ArrayList class java.lang.String class java.lang.Integer As you see it will show the type of the object which … Read more
Usually, one would call the reduce method using Math.max(int, int) as follows: reduce(new IntBinaryOperator() { int applyAsInt(int left, int right) { return Math.max(left, right); } }); That requires a lot of syntax for just calling Math.max. That’s where lambda expressions come into play. Since Java 8 it is allowed to do the same thing in a much shorter way: reduce((int … Read more
Is there a simple way to convert a LocalDate (introduced with Java 8) to java.util.Date object? By ‘simple’, I mean simpler than this Nope. You did it properly, and as concisely as possible. java.util.Date.from( // Convert from modern java.time class to troublesome old legacy class. DO NOT DO THIS unless you must, to inter operate … Read more
Where to get the tools.jar to use with the Java 8 jdk early release
