《java8函数式编程》第三章课后习题

import java.util.ArrayList;

import java.util.LinkedList;

import java.util.List;

import java.util.Set;

import java.util.stream.Collectors;

import java.util.stream.Stream;

/**

@Author: cxh
@CreateTime: 17/12/14 20:47
@ProjectName: JavaBaseTest
<测试类></>

*/

public class Test {

public static void main(String[] args) {

//1.1求和

Stream stream;

List list=new LinkedList<>();

list.add(1);list.add(2);list.add(4);

stream=list.stream();

System.out.println(addUp(stream));

System.out.println("---------1.1输出结束--------------");
    //1.2返回字符串列表,包含艺术家的姓名和国籍
    List<String> nameAndOriginal;
    ArrayList<Artist> nao=new ArrayList<>();
    nao.add(new Artist("Holino",null,"Landon"));
    nao.add(new Artist("Luciba","China"));
    nao.add(new Artist("Luciyi","Australia"));
    nameAndOriginal=getNameAndOriginal(nao);
    for(String str:nameAndOriginal)
        System.out.println(str);
    System.out.println("---------1.2输出结束-----------------");

    //1.3返回最多包含3首歌曲的专辑组成的列表
    Set<Album> albums;
    ArrayList<Album> albumArrayList=new ArrayList<>();
    for(int i=1;i<6;i++){
        albumArrayList.add(new Album("qisi",getTracks(i),getArtists()));
    }
    Set<Album> albumSet=getAlbums(albumArrayList);
    for(Album a:albumSet){
        System.out.println("name is: "+a.getName()+"tracks`size is:"+a.getTracks().size());
    }
    System.out.println("---------1.3输出结束-----------------");
}
//1.1计算流中所有数字之和
private static  int addUp(Stream<Integer> numbers){
    return numbers.reduce(0,(acc,elemeent)->(acc+elemeent)).intValue();
}

//1.2返回字符串列表,包含艺术家的姓名和国籍
private static List<String> getNameAndOriginal(ArrayList<Artist> list){
    List<String> res;
    res=list.stream()
    .map(artist -> "name is: "+artist.getName()+" and original is: "+artist.getOriginal()+",")
    .collect(Collectors.toList());
    return res;
}
//1.3返回最多包含3首歌曲的专辑组成的列表
private static Set<Album> getAlbums(ArrayList<Album> list){
    Set<Album> res;
    res=list.stream()
            .filter(album -> album.getTracks().size()<=3)
            .collect(Collectors.toSet());
    return res;
}

//获取艺术家列表
private static ArrayList<Artist> getArtists(){
    ArrayList<Artist> res=new ArrayList<>();
    for(int i=0;i<5;i++){
        ArrayList<String> members=new ArrayList<>();
        members.add("lili");
        members.add("zhouqing");
        res.add(new Artist("ladygaga",members,"europe"));
    }
    return res;
}
//获取歌曲列表
private static ArrayList<Track> getTracks(int count){
    ArrayList<Track> tracks=new ArrayList<>();
    for(int i=0;i<count;i++){
        Track track=new Track("qicaishiguang",10);
        tracks.add(track);
    }
    return tracks;
}
}
//输出结果：

7

---------1.1输出结束--------------

name is: Holino and original is: Landon,name is: Luciba and original is: China,name is: Luciyi and original is: Australia,---------1.2输出结束-----------------

name is: qisi and  the tracks size is:2 name is: qisi and  the tracks size is:3

name is: qisi and  the track`s size is:1

---------1.3输出结束-----------------
Process finished with exit code 0

import java.util.ArrayList;

/**

@Author: cxh
@CreateTime: 17/12/14 20:47
@ProjectName: JavaBaseTest
<测试类></>

*/

public class Test {

public static void main(String[] args) {

ArrayList artists=getArtists();

//输出artists

System.out.println("---------以下为各个Artist中的成员个数----------");

for(Artist a:artists){

System.out.print(a.getMembers().size()+",");

}

System.out.println();
    System.out.println("---------下面为使用Lambda表达式求各个Artist中成员的总数--------");
    int res=artists.stream().map(artist -> artist.getMembers().size())
            .reduce(0,members)->(acc+members))
            .intValue();
    System.out.println(res);
}

//获取艺术家列表
private static ArrayList<Artist> getArtists(){
    ArrayList<Artist> res=new ArrayList<>();
    for(int i=0;i<6;i++){
        ArrayList<String> members=new ArrayList<>();
        for(int j=-1;j<i;j++){
            members.add("lili"+i);
        }
        res.add(new Artist("ladygaga"+i,"europe"+i));
    }
    return res;
}
}
//运行结果

---------以下为各个Artist中的成员个数----------

1,2,3,4,5,6,---------下面为使用Lambda表达式求各个Artist中成员的总数--------

21
Process finished with exit code 0

import java.util.ArrayList;

/**

@Author: cxh
@CreateTime: 17/12/14 20:47
@ProjectName: JavaBaseTest
<测试类></>

*/

public class Test {

public static void main(String[] args) {

String str="123qwe";

long res;

res=str.chars().filter(c->c>=97 &&c<=122)

.count();

System.out.println(res);

/**

String的chars()方法分析

*/

int[] test=str.chars().toArray();

for(int i:test)

System.out.println(i);

/**
输出:
49 
50
51
113
119
101


所以,从输出结果可以知道:chars()方法,返回的是字符串中所有字符对应的assii码值.
通过chars()源码可以知道:JDK1.8才开始有这个方法.它返回的是int类型的数据流:IntStream

*/

}

}

//输出结果

3
Process finished with exit code 0

import java.util.ArrayList;

import java.util.Comparator;

/**

@Author: cxh
@CreateTime: 17/12/14 20:47
@ProjectName: JavaBaseTest
<测试类></>

*/

public class Test {

public static void main(String[] args) {

ArrayList list=new ArrayList<>();

for(int i=1;i<10;i++){

StringBuilder sb=new StringBuilder();

for(int j=0;j<=i;j++){

sb.append("d");

}

list.add(sb.toString());

}

String max=list.stream().max(Comparator.comparing(s ->getCount(s) )).get();

System.out.println(max);

}
/**
 * 获取字符串str中包含的小写字母个数
 * @param str
 * @return
 */
private static long getCount(String str){
    return str.chars().filter(c->c>=97 &amp;&amp; c<=122).count();
}
}
//输出结果

dddddddddd
Process finished with exit code 0

（编辑：李大同）

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