layout: post title: “02-26-java8新特性” date: 2019-02-26 12:11:30 +0800

  1. lambda 和 函数表达式 函数接口 lambda 单函数表达式 单函数接口,并为接口增加注解@FunctionalInterface

lambda示例:

        Arrays.asList( "a", "b", "d" ).forEach(System.out::print);

        Arrays.asList( "a", "b", "d" ).forEach( e -> System.out.print( e ) );

        Arrays.asList( "a", "b", "d" ).forEach( e -> {System.out.print( e );} );

        Arrays.asList( "a", "b", "d" ).forEach( ( String e ) -> System.out.print( e ) );

        Arrays.asList( "a", "b", "d" ).forEach(new Consumer<String>() {
            @Override
            public void accept(String s) {
                System.out.println(s);
            }
        });

函数传递

   public static boolean isGreenApple( Apple apple )
    {
        return("green".equals( apple.getColor() ) );
    }


    public static boolean isHeavyApple( Apple apple )
    {
        return(apple.getWeight() > 150);
    }


    public interface Predicate<T>{
        boolean test( T t );
    }

    static List<Apple> filterApples( List<Apple> inventory, Predicate<Apple> p )
    {
        List<Apple> result = new ArrayList<>();
        for ( Apple apple : inventory )
        {
            if ( p.test( apple ) )
            {
                result.add( apple );
            }
        }
        return(result);
    }
    //main
    filterApples(inventory, Main::isGreenApple);
  1. 接口的默认方法和静态方法 ``` private interface Defaulable { // Interfaces now allow default methods, the implementer may or // may not implement (override) them. default String notRequired() { return “Default implementation”; }
    }

private static class DefaultableImpl implements Defaulable { }

private static class OverridableImpl implements Defaulable { @Override public String notRequired() { return “Overridden implementation”; } } private interface DefaulableFactory { // Interfaces now allow static methods static Defaulable create( Supplier< Defaulable > supplier ) { return supplier.get(); } } public static void main( String[] args ) { Defaulable defaulable = DefaulableFactory.create( DefaultableImpl::new ); System.out.println( defaulable.notRequired() );

defaulable = DefaulableFactory.create( OverridableImpl::new );
System.out.println( defaulable.notRequired() ); }


3 方法引用

public static class Car { public static Car create( final Supplier< Car > supplier ) { return supplier.get(); }

public static void collide( final Car car ) {
    System.out.println( "Collided " + car.toString() );
}
 
public void follow( final Car another ) {
    System.out.println( "Following the " + another.toString() );
}
 
public void repair() {   
    System.out.println( "Repaired " + this.toString() );
} } // 引用的类型是构造器引用 final Car car = Car.create( Car::new ); // 静态方法引用 cars.forEach( Car::collide ); // 成员方法的引用 cars.forEach( Car::repair ); // 实例对象的成员方法的引用 final Car police = Car.create( Car::new ); cars.forEach( police::follow );


4. 加入函数的参数名称

5. Optional进行可非空内容包装

    Optional< String > fullName = Optional.ofNullable( null );
    System.out.println( "Full Name is set? " + fullName.isPresent() );
    System.out.println( "Full Name: " + fullName.orElseGet( () -> "[none]" ) );
    System.out.println( fullName.map( s -> "Hey " + s + "!" ).orElse( "Hey Stranger!" ) ); ``` 6. Streams

使流处理更加简单,parallel增加流并行能力

  1. Date/Time API

优化日期处理能力

  1. 类依赖分析器：jdeps