java8学习（一）

浅浅的花香味﹌ 2022-05-21 04:17 157阅读 0赞

**行为参数化**

package com.huhu.test.helloword.java8;
    
    /** * @author :小虎 * @date :2018/6/29 */
    
    
    public class Apple { 
        private String color;
        private int weight;
    
        public Apple(int weight,String color) {
            this.color = color;
            this.weight = weight;
        }
    
        public String getColor() {
    
            return color;
        }
    
        public void setColor(String color) {
            this.color = color;
        }
    
        public int getWeight() {
            return weight;
        }
    
        public void setWeight(int weight) {
            this.weight = weight;
        }
    }

package com.huhu.test.helloword.java8;
    
    /** * @author :小虎 * @date :2018/6/29 */
    
    
    public class AppleGreenColorPredicate implements ApplePredicate{ 
        @Override
        public boolean test(Apple apple){
            return "green".equals(apple.getColor());
        }
    }

package com.huhu.test.helloword.java8;
    
    /** * @author :小虎 * @date :2018/6/29 */
    
    
    public class AppleHeavyWeightPredicate implements ApplePredicate{ 
        @Override
        public boolean test(Apple apple){
            return apple.getWeight() > 150;
        }
    }

package com.huhu.test.helloword.java8;
    
    /** * @author :小虎 * @date :2018/6/29 */
    
    
    public interface ApplePredicate{ 
        boolean test (Apple apple);
    }

package com.huhu.test.helloword.java8;
    
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.List;
    
    /** * @author :小虎 * @date :2018/6/29 */
    
    
    public class Test { 
        public static void main(String[] args) {
            List<Apple> inventory = Arrays.asList(new Apple(80,"green"),
                    new Apple(155, "green"),
                    new Apple(120, "red"));
            List<Apple> heavyApples = filterApples(inventory, new AppleHeavyWeightPredicate());
            List<Apple> greenApples = filterApples(inventory, new AppleGreenColorPredicate());
    
            System.out.println(heavyApples.size());
            System.out.println(greenApples.size());
    
        }
        public static List<Apple> filterApples(List<Apple> inventory, ApplePredicate p){
            List<Apple> result = new ArrayList<>();
            for(Apple apple: inventory){
                if(p.test(apple)){
                    result.add(apple);
                }
            }
            return result;
        }
    }

**改进尝试一(匿名类)**

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

**改进尝试二(Lambda 表达式)**

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

**改进尝试三(将 List 类型抽象化)**

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

List<Apple> redApples =filter(inventory, (Apple apple) -> "red".equals(apple.getColor())); List<Integer> evenNumbers =filter(numbers, (Integer i) -> i % 2 == 0);

**Comparator**

inventory.sort((Apple a1, Apple a2) -> a1.getWeight().compareTo(a2.getWeight()));

**Runnable**

Thread t = new Thread(() -> System.out.println("Hello world"));

**函数式接口**

> 一言以蔽之， 函数式接口就是只定义一个抽象方法的接口。你已经知道了Java API中的一些  
> 其他函数式接口，如我们在第2章中谈到的Comparator和Runnable

public interface Comparator<T> { 
        int compare(T o1, T o2);
    }
    public interface Runnable{ 
        void run();
    }
    public interface ActionListener extends EventListener{ 
        void actionPerformed(ActionEvent e);
    }
    public interface Callable<V>{ 
        V call();
    }
    public interface PrivilegedAction<V>{ 
        V run();
    }

> Lambda表达式允许你直接以内联的形式为函数式接口的抽象方法提供实现， 并把整个表达式作为函数式接口的实例（具体说来，是函数式接口一个具体实现的实例）。