Javaのstream().map()でListの型を変換する

2019.08.30

Javaのstream().map()でListの型を変換する

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) throws Exception {
        List<Fruit> fruitsBucket = new ArrayList<>();

        fruitsBucket.add(new Fruit("りんご"));
        fruitsBucket.add(new Fruit("みかん"));
        fruitsBucket.add(new Fruit("オレンジ"));

        List<Juice> refrigerator = fruitsBucket.stream()
                .map(f -> new Juice(f.type))
                .collect(Collectors.toList());

        System.out.println("fruitsBucket : " + fruitsBucket);
        System.out.println("refrigerator : " + refrigerator);
    }
}

class Fruit {
    public String type;

    public Fruit(String type) {
        this.type = type;
    }

    public String toString() {
        return type;
    }
}

class Juice {
    public String type;

    public Juice(String type) {
        this.type = type;
    }

    public String toString() {
        return type + "ジュース";
    }
}

import java.util.*;

import java.util.stream.Collectors;

public class Main {

public static void main(String[] args) throws Exception {

List<Fruit> fruitsBucket = new ArrayList<>();

fruitsBucket.add(new Fruit("りんご"));

fruitsBucket.add(new Fruit("みかん"));

fruitsBucket.add(new Fruit("オレンジ"));

List<Juice> refrigerator = fruitsBucket.stream()

.map(f -> new Juice(f.type))

.collect(Collectors.toList());

System.out.println("fruitsBucket : " + fruitsBucket);

System.out.println("refrigerator : " + refrigerator);

}

class Fruit {

public String type;

public Fruit(String type) {

this.type = type;

}

public String toString() {

return type;

}

class Juice {

public String type;

public Juice(String type) {

this.type = type;

}

public String toString() {

return type + "ジュース";

}

fruitsBucket : [りんご, みかん, オレンジ]
refrigerator : [りんごジュース, みかんジュース, オレンジジュース]

1 2	fruitsBucket : [りんご, みかん, オレンジ] refrigerator : [りんごジュース, みかんジュース, オレンジジュース]

2019.08.26

filterで引数の配列から偶数の要素に絞った新たな配列を得る

従来のforより短くかけることを認めざるを得ない

'use strict'
/* 引数の配列から偶数の要素に絞った新たな配列を得る */
const p = console.log
const a = [-2, -1, 0, 1, 2, 3, 4, 5]
p(a)

/* for */
const getOnlyEvenArrayByFor = a => {
  const b = []
  let i = 0;
  for (const n of a) {
    if (n % 2 == 0) {
      b[i++] = n
    }
  }
  return b
}

/* filter */
const getOnlyEvenArrayByFilter = a => {
  return a.filter(n => n % 2 == 0)
}
const getOnlyEvenArrayByFilterOneLiner = a => a.filter(n => n % 2 == 0)

p(getOnlyEvenArrayByFor(a))
p(getOnlyEvenArrayByFilter(a))
p(getOnlyEvenArrayByFilterOneLiner(a))

'use strict'

/* 引数の配列から偶数の要素に絞った新たな配列を得る */

const p = console.log

const a = [-2, -1, 0, 1, 2, 3, 4, 5]

p(a)

/* for */

const getOnlyEvenArrayByFor = a => {

const b = []

let i = 0;

for (const n of a) {

if (n % 2 == 0) {

b[i++] = n

}

return b

}

/* filter */

const getOnlyEvenArrayByFilter = a => {

return a.filter(n => n % 2 == 0)

}

const getOnlyEvenArrayByFilterOneLiner = a => a.filter(n => n % 2 == 0)

p(getOnlyEvenArrayByFor(a))

p(getOnlyEvenArrayByFilter(a))

p(getOnlyEvenArrayByFilterOneLiner(a))

[ -2, -1, 0, 1, 2, 3, 4, 5 ]
[ -2, 0, 2, 4 ]
[ -2, 0, 2, 4 ]
[ -2, 0, 2, 4 ]

[ -2, -1, 0, 1, 2, 3, 4, 5 ]

[ -2, 0, 2, 4 ]

2019.08.13

alertでconsoleの内容が見たい

/* alertでconsoleの内容が見たい */
const main = () => {
  let buf: string = "";

  const p = (arg: any) => {
    if ("object" === typeof arg) {
      arg = JSON.stringify(arg);
    }
    buf += arg += "\n";
    console.log(arg);
  };

  const disp = () => {
    alert(buf);
  };

  const sub = () => {
    const a = { あ: "a", い: "i" };

    p('"hello" : ' + "hello");
    p("123 : " + 123);
    p("typeof a : " + typeof a);
    p("a : " + a);
    p(a);
  };

  sub();
  disp();
};
main();

/* alertでconsoleの内容が見たい */

const main = () => {

let buf: string = "";

const p = (arg: any) => {

if ("object" === typeof arg) {

arg = JSON.stringify(arg);

}

buf += arg += "\n";

console.log(arg);

};

const disp = () => {

alert(buf);

};

const sub = () => {

const a = { あ: "a", い: "i" };

p('"hello" : ' + "hello");

p("123 : " + 123);

p("typeof a : " + typeof a);

p("a : " + a);

p(a);

};

sub();

disp();

};

main();

"hello" : hello
123 : 123
typeof a : object
a : [object Object]
{"あ":"a","い":"i"}

"hello" : hello

123 : 123

typeof a : object

a : [object Object]

{"あ":"a","い":"i"}

https://www.typescriptlang.org/play/#code/PQKgBAhgNgpgTgF0OYMBjA9gOwM5toOwZBQxUE7tQGQZBoyMH0GQEQYwRgAodbBMAWwgEsMwBeMACgCUvAHxgA3vTBhYLAEYBXAGYAuMFgRwuAc15gARPoDc9KWCYawABz38IcbWogYAnsJ5jJ06RyUD9aHIAVjAoCPq8PHwILlYwaH722sJe3tJJegBSAMoA8gByAHQaWhjavi52DoImaQC+ZtKKfgDUfBltBgA6GMaN5pg4sIVQaNpVybVgdSZmFiwAJhxYNnxCohL90PAI-M01ZjOm0vPqCnK27p79pxB64mCAQgxq+hD6ADRgVC8cEUf9Vn4AHJ9AALGBQUYRNRAsAtAzgyFofQHNKA-QARgATABmMAvOFgbE41HedExOIJSD4gyEinxRKk6Tou4E+EQJnWOyk-7SLDnIRTJYrQX0I7sLiioA

2019年 8月の投稿一覧