[Ken Kousen]Modern Java Recipes

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关键词：Recipes Modern Recipe Moder mode Java

1. Example 1-1. Anonymous Inner Class Implementation of Runnable
   
2. public class RunnableDemo {
   
3. public static void main(String[] args) {
   
4. // Works in Java 7 or earlier:
   
5. new Thread(new Runnable() {
   
6. @Override
   
7. public void run() {
   
8. System.out.println(
   
9. "inside runnable using an anonymous inner class"
   
10. }
    
11. }).start();
    
12. }
    
13. }

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Example 1-2. Using a lambda expression in a Thread constructor

1. public class RunnableDemo {
   
2. public static void main(String[] args) {
   
3. new Thread(() -> System.out.println(
   
4. "inside Thread constructor using lambda")).start();
   
5. }
   
6. }
   
7. The syntax uses an arrow to separate the arguments (since there are zero
   
8. arguments here, only a pair of empty parentheses is used) from the body. In this
   
9. case, the body consists of a single line, so no braces are required. This is
   
10. known as an expression lambda. Whatever value the expression evaluates to is
    
11. returned automatically. In this case, since println returns void, the return
    
12. from the expression is also void, which matches the return type of the run
    
13. method.

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Example 1-3. Assigning a lambda expression to a variable

1. Example 1-3. Assigning a lambda expression to a variable
   
2. public class RunnableDemo {
   
3. public static void main(String[] args) {
   
4. Runnable r = () -> System.out.println(
   
5. "lambda expression implementing the run method");
   
6. new Thread(r).start();
   
7. }
   
8. }

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Example 1-4. An anonymous inner class implementation of FilenameFilter

1. Example 1-4. An anonymous inner class implementation of FilenameFilter
   
2. import java.io.File;
   
3. import java.io.FilenameFilter;
   
4. import java.util.Arrays;
   
5. public class UseFilenameFilter {
   
6. public static void main(String[] args) {
   
7. File directory = new File("./src/main/java");
   
8. // Anonymous inner class
   
9. String[] names = directory.list(new FilenameFilter() {
   
10. @Override
    
11. public boolean accept(File dir, String name) {
    
12. return name.endsWith(".java");
    
13. }
    
14. });
    
15. System.out.println(Arrays.asList(names));
    
16. }
    
17. }

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Example 1-5. Lambda expression implementing FilenameFilter

1. Example 1-5. Lambda expression implementing FilenameFilter
   
2. import java.io.File;
   
3. import java.io.FilenameFilter;
   
4. import java.util.Arrays;
   
5. public class UseFilenameFilter {
   
6. public static void main(String[] args) {
   
7. File directory = new File("./src/main/java");
   
8. // Use lambda expression instead
   
9. String[] names = directory.list((dir, name) -> name.endsWith
   
10. System.out.println(Arrays.asList(names));
    
11. }
    
12. }

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1. Example 4-1. Reference implementation of Stream.of
   
2. @SafeVarargs
   
3. public static<T> Stream<T> of(T... values) {
   
4. return Arrays.stream(values);
   
5. }
   
6. Tip
   
7. The @SafeVarargs annotation is part of Java generics. It comes up when you
   
8. have an array as an argument, because it is possible to assign a typed array to
   
9. an Object array and then violate type safety with an added element. The
   
10. @SafeVarargs annotation tells the compiler that the developer promises not to
    
11. do that. See [Link to Come] for additional details.

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1. Example 4-2. Creating a stream using Stream.of
   
2. String names = Stream.of("Gomez", "Morticia", "Wednesday", "Pugsley"
   
3. .collect(Collectors.joining(","));
   
4. System.out.println(names);
   
5. // prints Gomez,Morticia,Wednesday,Pugsley
   
6. The API also includes an overloaded of method that takes a single element T
   
7. t. This method returns a singleton sequential stream containing a single
   
8. element.

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