lambda表達(dá)式如何正確的在Java8項(xiàng)目中使用

//Before Java 8:
new Thread(new Runnable() {
 @Override
 public void run() {
  System.out.println("Before Java8 ");
 }
}).start();
//Java 8 way:
new Thread(() -> System.out.println("In Java8!"));
// Before Java 8:
JButton show = new JButton("Show");
show.addActionListener(new ActionListener() {
  @Override
  public void actionPerformed(ActionEvent e) {
   System.out.println("without lambda expression is boring");
  }
  });
// Java 8 way:
show.addActionListener((e) -> {
 System.out.println("Action !! Lambda expressions Rocks");
});

//Prior Java 8 :
List features = Arrays.asList("Lambdas", "Default Method", 
"Stream API", "Date and Time API");
for (String feature : features) {
 System.out.println(feature);
}
//In Java 8:
List features = Arrays.asList("Lambdas", "Default Method", "Stream API",
 "Date and Time API");
features.forEach(n -> System.out.println(n));
// Even better use Method reference feature of Java 8
// method reference is denoted by :: (double colon) operator
// looks similar to score resolution operator of C++
features.forEach(System.out::println);

Output:
Lambdas
Default Method
Stream API
Date and Time API

public static void main(args[]){
 List languages = Arrays.asList("Java", "Scala", "C++", "Haskell", "Lisp");
 System.out.println("Languages which starts with J :");
 filter(languages, (str)->str.startsWith("J"));
 System.out.println("Languages which ends with a ");
 filter(languages, (str)->str.endsWith("a"));
 System.out.println("Print all languages :");
 filter(languages, (str)->true);
 System.out.println("Print no language : ");
 filter(languages, (str)->false);
 System.out.println("Print language whose length greater than 4:");
 filter(languages, (str)->str.length() > 4);
}
 public static void filter(List names, Predicate condition) {
 names.stream().filter((name) -> (condition.test(name)))
  .forEach((name) -> {System.out.println(name + " ");
 });
 }

Output:
Languages which starts with J :
Java
Languages which ends with a
Java
Scala
Print all languages :
Java
Scala
C++
Haskell
Lisp
Print no language :
Print language whose length greater than 4:
Scala
Haskell

final BigDecimal totalOfDiscountedPrices = prices.stream()
.filter(price -> price.compareTo(BigDecimal.valueOf(20)) > 0)
.map(price -> price.multiply(BigDecimal.valueOf(0.9)))
.reduce(BigDecimal.ZERO,BigDecimal::add);
System.out.println("Total of discounted prices: " + totalOfDiscountedPrices);

// simple check against empty strings
public static int check(String s) {
 if (s.equals("")) {
  throw new IllegalArgumentException();
 }
 return s.length();
}
//map names to lengths
List lengths = new ArrayList();
for (String name : Arrays.asList(args)) {
 lengths.add(check(name));
}

at LmbdaMain.check(LmbdaMain.java:19)
at LmbdaMain.main(LmbdaMain.java:34)

Stream lengths = names.stream().map(name -> check(name));
 at LmbdaMain.check(LmbdaMain.java:19)
at LmbdaMain.lambda$0(LmbdaMain.java:37)
at LmbdaMain$$Lambda$1/821270929.apply(Unknown Source)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.LongPipeline.reduce(LongPipeline.java:438)
at java.util.stream.LongPipeline.sum(LongPipeline.java:396)
at java.util.stream.ReferencePipeline.count(ReferencePipeline.java:526)
at LmbdaMain.main(LmbdaMain.java:39)