java8 代码传递

在一群苹果中筛选出自己想要的苹果

java8之前

package com.chen.java8;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * 代码传递
 * 
 * @author jj
 *
 */
public class Charpter_02 {
	public static void main(String[] args) {
		List<Apple> apples = new ArrayList<>();
		apples.addAll(Arrays.asList(new Apple("green", 4d),new Apple("red", 4d),new Apple("green", 8d)));
		List<Apple> greenApples = getGreenApples(apples);
		greenApples.forEach((Apple apple)->System.out.println(apple.toString()));
	}
	
	//筛选出绿色的苹果
	public static List<Apple> getGreenApples(List<Apple> apples) {
		List<Apple> greenApples = new ArrayList<>();
		for (Apple apple : apples) {
			if(apple.getColor().equals("green")) {
				greenApples.add(apple);
			}
		}
		return greenApples;
	}
}


class Apple {
	private String color;
	private Double weight;
	public Apple(String color, Double weight) {
		super();
		this.color = color;
		this.weight = weight;
	}
	public String getColor() {
		return color;
	}
	public void setColor(String color) {
		this.color = color;
	}
	public Double getWeight() {
		return weight;
	}
	public void setWeight(Double weight) {
		this.weight = weight;
	}
	@Override
	public String toString() {
		return "Apple [color=" + color + ", weight=" + weight + "]";
	}
	
}

java8

package com.chen.java8;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * 代码传递
 * 
 * @author jj
 *
 */
public class Charpter_02 {
	public static void main(String[] args) {
		List<Apple> apples = new ArrayList<>();
		apples.addAll(Arrays.asList(new Apple("green", 4d),new Apple("red", 4d),new Apple("green", 8d)));
		List<Apple> greenApples = getApples(apples, Apple::isGreenApple);
		greenApples.forEach((Apple apple)->System.out.println(apple.toString()));
	}
	
	//筛选出绿色的苹果
//	public static List<Apple> getGreenApples(List<Apple> apples) {
//		List<Apple> greenApples = new ArrayList<>();
//		for (Apple apple : apples) {
//			if(apple.getColor().equals("green")) {
//				greenApples.add(apple);
//			}
//		}
//		return greenApples;
//	}
	
	//筛选出符合条件的苹果
	public static List<Apple> getApples(List<Apple> apples, Predicate<Apple> p){
		List<Apple> rApples = new ArrayList<>();
		for (Apple apple : apples) {
			if(p.test(apple)) {
				rApples.add(apple);
			}
		}
		return rApples;
	}
}


class Apple {
	private String color;
	private Double weight;
	public Apple(String color, Double weight) {
		super();
		this.color = color;
		this.weight = weight;
	}
	public String getColor() {
		return color;
	}
	public void setColor(String color) {
		this.color = color;
	}
	public Double getWeight() {
		return weight;
	}
	public void setWeight(Double weight) {
		this.weight = weight;
	}
	@Override
	public String toString() {
		return "Apple [color=" + color + ", weight=" + weight + "]";
	}
	
	public static boolean isGreenApple(Apple apple) {
		return "green".equals(apple.getColor());
	}
	
	public static boolean isWeightApple(Apple apple) {
		return apple.getWeight()>5d;
	}
}

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

甚至可以将筛选语句改为

//		List<Apple> greenApples = getApples(apples, Apple::isGreenApple);
		List<Apple> greenApples = getApples(apples, (Apple a) -> a.getColor().equals("red"));