Java8新特性

Java8新特性

Project 01

• 给出了行为参数化传递代码的方式

1. 定义一个标准的谓词模板

public interface ApplePredicate{
    boolean test (Apple apple);
}

2. 用ApplePredicate的多个实现代表不同的选择标准

public class AppleHeavyWeightPredicate implements ApplePredicate{ 
    public boolean test(Apple apple){
        return apple.getWeight() > 150; 
    }
}
public class AppleGreenColorPredicate implements ApplePredicate{
    public boolean test(Apple apple){
        return "green".equals(apple.getColor());
    }
}

3. 设置抽象条件筛选

public static List filterApples(List inventory,ApplePredicate p){
    List result = new ArrayList<>();
    for(Apple apple: inventory){
        if(p.test(apple)){ 
            result.add(apple);
        } 
    }
    return result;
}

4. 代码传递行为

public class AppleRedAndHeavyPredicate implements ApplePredicate{ 
    public boolean test(Apple apple){
        return "red".equals(apple.getColor()) && apple.getWeight() > 150;
    } 
}
List redAndHeavyApples = filterApples(inventory, new AppleRedAndHeavyPredicate());

5. 使用匿名类

List redApples = filterApples(inventory, new ApplePredicate() { 
    public boolean test(Apple apple){
        return "red".equals(apple.getColor());
    });
}

6. 使用Lambda表达式

List result = filterApples(inventory, (Apple apple) -> "red".equals(apple.getColor()));

7. 将List抽象化

public interface Predicate{
    boolean test(T t);
}
public static  List filter(List list, Predicate p){
    List result = new ArrayList<>();
    for(T e: list){
        if(p.test(e)){
            result.add(e);
        }
    } 
    return result;
}

Project 02

• 匿名类与Lambda表达式的使用

• 使用函数式接口

1. java.util.function.Predicate接口定义了一个名叫test的抽象方法，它接受泛型 T对象，并返回一个boolean

@FunctionalInterface
public interface Predicate{
    boolean test(T t);
}
public static  List filter(List list, Predicate p) {
    List results = new ArrayList<>();
    for(T s: list){
        if(p.test(s)){
            results.add(s);
        } 
    }
    return results;
}
Predicate nonEmptyStringPredicate = (String s) -> !s.isEmpty(); List nonEmpty = filter(listOfStrings, nonEmptyStringPredicate);

2. java.util.function.Consumer定义了一个名叫accept的抽象方法，它接受泛型T的对象，没有返回(void)。你如果需要访问类型T的对象，并对其执行某些操作，就可以使用这个接口。

@FunctionalInterface
public interface Consumer{
    void accept(T t);
}
public static  void forEach(List list, Consumer c){
    for(T i: list){ 
        c.accept(i);
    }
}
forEach(Arrays.asList(1,2,3,4,5), (Integer i) -> System.out.println(i));

3. java.util.function.Function接口定义了一个叫作apply的方法，它接受一个泛型T的对象，并返回一个泛型R的对象。如果你需要定义一个Lambda，将输入对象的信息映射到输出，就可以使用这个接口。

@FunctionalInterface
public interface Function{
    R apply(T t);
}
public static  List map(List list, Function f) {
    List result = new ArrayList<>();
    for(T s: list){
       result.add(f.apply(s)); 
    }
    return result;
}
List l = map(Arrays.asList("lambdas","in","action"), (String s) -> s.length());

Project 03

• 引入流Stream

List heavyApples = inventory.stream().filter((Apple a) -> a.getWeight() > 150).collect(toList());

• 如何使用Stream
• 如何用流收集数据
• 并行数据处理

List heavyApples = inventory.parallelStream().filter((Apple a) -> a.getWeight() > 150) .collect(toList());

Project 04

• 使用Java8新特性重构代码
• Optional
• CompletableFuture

源码参考

Java8InAction