Java8之集合(Collection)遍历 forEach()、stream()

package java8.collections;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.stream.Collectors;

import org.junit.Before;
import org.junit.Test;

public class ForEach {
    
    private List<String> list = new ArrayList<>();
 
    @Before
    public void initData() {
        list.add("Java 1.5");
        list.add("Java 1.6");
        list.add("Scala");
        list.add("Python");
        list.add("Html");
        list.add("css");
        list.add("JavaScript");
        list.add("js");
        list.add("Hadoop");
        list.add("C");
        list.add("redis");
        list.add("Java 1.7");
        list.add("Java 1.8");
 
    }
 
    /**
     * 在Java8之前的遍历方式
     */
    @Test
    public void testErgodicWayBeforeJava8() {
        System.out.println("\nBefore JAVA8 ===================================>");
        System.out.println(">>>> for loop:");
        for (int i = 0; i < list.size(); i++) {
            System.out.println("list.get(i) = " + list.get(i));
        }
        System.out.println(">>>> for loop enhanced:");
        for (String ele : list) {
            System.out.println("ele = " + ele);
        }
        System.out.println(">>>> iterator:");
        Iterator<String> iterator = list.iterator();
        while (iterator.hasNext()){
            System.out.println("iterator.next() = " + iterator.next());
        }
    }
 
    /**
     * 在Java8中的遍历方式
     */
    @Test
    public void testCollection_forEach_Java8() {
        System.out.println("\nJAVA8:::Collection.forEach ======================>");
        list.forEach(System.out::println);
    }
    
    @Test
    public void testCollection_stream_map_Java8() {
        System.out.println("\nJAVA8:::Collection.stream.map ==================>");
        list.stream()
            .map(item -> "Mapped_Value_" + item)
            .collect(Collectors.toList()).stream()
            .forEach(System.out::println);
    }
    
    @Test
    public void testCollection_stream_filter_map_Java8() {
        System.out.println("\nJAVA8:::Collection.stream.filter.map ==========>");
        list.stream()
            .filter(item -> item.contains("Java"))
            .map(item -> "Mapped_Value_" + item)
            .collect(Collectors.toList()).stream()
            .forEach(System.out::println);
    }
    
}

输出结果：


Before JAVA8 ===================================>
>>>> for loop:
list.get(i) = Java 1.5
list.get(i) = Java 1.6
list.get(i) = Scala
list.get(i) = Python
list.get(i) = Html
list.get(i) = css
list.get(i) = JavaScript
list.get(i) = js
list.get(i) = Hadoop
list.get(i) = C
list.get(i) = redis
list.get(i) = Java 1.7
list.get(i) = Java 1.8
>>>> for loop enhanced:
ele = Java 1.5
ele = Java 1.6
ele = Scala
ele = Python
ele = Html
ele = css
ele = JavaScript
ele = js
ele = Hadoop
ele = C
ele = redis
ele = Java 1.7
ele = Java 1.8
>>>> iterator:
iterator.next() = Java 1.5
iterator.next() = Java 1.6
iterator.next() = Scala
iterator.next() = Python
iterator.next() = Html
iterator.next() = css
iterator.next() = JavaScript
iterator.next() = js
iterator.next() = Hadoop
iterator.next() = C
iterator.next() = redis
iterator.next() = Java 1.7
iterator.next() = Java 1.8

JAVA8:::Collection.forEach ======================>
Java 1.5
Java 1.6
Scala
Python
Html
css
JavaScript
js
Hadoop
C
redis
Java 1.7
Java 1.8

JAVA8:::Collection.stream.map ==================>
Mapped_Value_Java 1.5
Mapped_Value_Java 1.6
Mapped_Value_Scala
Mapped_Value_Python
Mapped_Value_Html
Mapped_Value_css
Mapped_Value_JavaScript
Mapped_Value_js
Mapped_Value_Hadoop
Mapped_Value_C
Mapped_Value_redis
Mapped_Value_Java 1.7
Mapped_Value_Java 1.8

JAVA8:::Collection.stream.filter.map ==========>
Mapped_Value_Java 1.5
Mapped_Value_Java 1.6
Mapped_Value_JavaScript
Mapped_Value_Java 1.7
Mapped_Value_Java 1.8



















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