2024. 7. 17. (수) 슈퍼코딩 부트캠프 Day 39 / 주특기 4주차

 

1.StreamAPI 중간연산

• 필터링 : filter()/ 조건식 통과하는 요소만 남음, distinct() / 중복되는 요소 제거
• 변화 : map() / 특정 함수에 매핑, 새로운 요소 반환
• 제한 : limit(max) / 최대요소갯수 지정, 스트림제한 , skip(n) / 처음 n개 요소 제외, 스트림 재생성
• 정렬 : sorted() / 요소를 특정 정렬 순서에 따라 생성

package exercise.chapter_55;

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

public class StreamIntermediateOpsTest {
    public static void main(String[] args) {
        List<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Apple");
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");
        fruits.add("Mango");
        fruits.add("Grapes");
        fruits.add("WaterMelon");
        fruits.add("Pineapple");
        fruits.add("Strawberry");

        //filter : 특정 조건, ex. 길이가 6이상인 요소 선택
        fruits.stream().filter(fruit -> fruit.length() >= 6).forEach(fruit -> System.out.println("필터 적용 fruit : " + fruit));

        //distinct : 중복 요소 제거
        List<String> fruitList = fruits.stream().distinct().collect(Collectors.toList());
        System.out.println("중복 제거 전 : " + fruits);
        System.out.println("중복 제거 후 : " + fruitList);

        //map : 새로운 값으로 변환
        List<String> fruitListMap = fruits.stream().map(fruit -> fruit.toUpperCase()).collect(Collectors.toList());
        System.out.println("map 적용 후 : " + fruitListMap);
        List<Integer> fruitListLength = fruits.stream().map(fruit -> fruit.length()).collect(Collectors.toList());
        System.out.println("length map 적용 후 : " + fruitListLength);

        //limit : 최대 갯수 지정
        List<String> fruitList3 = fruits.stream().limit(3).collect(Collectors.toList());
        System.out.println("limit 적용 후 : " + fruitList3);

        //skip : 처음 n개 건너뛰고 선택
        List<String> fruitList4 = fruits.stream().skip(3).collect(Collectors.toList());
        System.out.println("skip 적용 후 : " + fruitList4);

        //sorted : 정렬
        List<String> fruitList5 = fruits.stream().sorted().collect(Collectors.toList());
        System.out.println("sorted 적용 후 : " + fruitList5);

        List<String> fruitList6 = fruits.stream().sorted((fruit1, fruit2) -> fruit1.length() - fruit2.length()).collect(Collectors.toList());
        System.out.println("길이 순 정렬 : " + fruitList6);
    }
}

 

• Java Comparator

@FunctionalInterface
public interface Comparator<T>{
    int compare(T o1, To2);
}
// 0 : o1 == o2
// 양수 : o1 > o2
// 음수 : o1 < o2

 

---

1. Java I/O Stream

• Stream의 방향 : 일방통행
• 입력스트림 : 어떤 대상으로부터 자료를 읽어들일때 사용하는 스트림
• 출력스트림 : 파일에 저장할때 출력 스트림 사용
• 스트림의 단위 : 바이트스트림 / 문자(2바이트) 스트림

 

• Console 입출력 받기
• System.in / System.out / System.err : System 클래스에 있는 정적 변수 ( in, out, err )

import java.io.IOException;

public class ConsoleTest {
    public static void main(String[] args) {
        //System.in으로 입력받기
        int i = 0;
        System.out.print("입력하세요 : ");
        try {
            StringBuilder sb = new StringBuilder();
            while ((i = System.in.read()) != '\n') {
                sb.append((char) i);
            }
            System.out.println(sb);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }


    }
}

 

package exercise.chapter_56;

import java.util.Scanner;

public class ScannerTest {
    //Scanner로 입력받기
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a name: ");
        String name = scanner.nextLine();
        System.out.print("Enter a job: ");
        String job = scanner.nextLine();
        System.out.print("Enter a age: ");
        int age = scanner.nextInt();

        System.out.printf("name : %s, job : %s, age : %d\n", name, job, age);
        scanner.close();
    }
}

 

---

2. 여러 종류 입출력

• file 입출력
• FileInputStream / FileOutputStream

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

public class FileInputStreamTest {
    public static void main(String[] args) {
        try (FileInputStream fis = new FileInputStream("src/exercise/chapter_56/test.txt")) {
            int i;
            while ((i = fis.read()) != -1) {
                System.out.print((char) i);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

 

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileOutputStreamTest {
    public static void main(String[] args) {
        String content = "this is content of file\n";
        try (FileOutputStream fos = new FileOutputStream("src/exercise/chapter_56/output.txt", true)) {
            //FileOutputStream 의 두번째 인자를 true로 하면 덮어쓰기가 아닌 append로 내용 추가.
            fos.write(content.getBytes());
            System.out.println("output file created");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

 

---

• FileReader / FileWriter

public class FileReaderTest {
    public static void main(String[] args) {
        try (FileReader fr = new FileReader("src/exercise/chapter_56/test.txt");) {
            int i;
            while ((i = fr.read()) != -1) {
                System.out.print((char) i);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

 

public class FileWriterTest {
    public static void main(String[] args) {
        String content = "한글 컨텐츠 입니다\n";
        try (FileWriter fw = new FileWriter("src/exercise/chapter_56/output_korean.txt")) {
            fw.write(content);
            System.out.println("output file created");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

 

---

• 이미지 출력 ImageIO

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class ImageIOTest {
    public static void main(String[] args) {
        String filePath = "src/exercise/chapter_56/oak.png";
        try {
            File file = new File(filePath);
            BufferedImage image = ImageIO.read(file);

            BufferedImage rotatedImage = rotateImage(image, 90);

            String outputFilePath = "src/exercise/chapter_56/oak_output.png";
            ImageIO.write(rotatedImage, "png", new File(outputFilePath));

            System.out.println("이미지 파일 생성 완료");

        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    private static BufferedImage rotateImage(BufferedImage image, double angle) {
        double radians = Math.toRadians(angle);
        double sin = Math.abs(Math.sin(radians));
        double cos = Math.abs(Math.cos(radians));

        int width = image.getWidth();
        int height = image.getHeight();

        int newWidth = (int) Math.round(width * cos + height * sin);
        int newHeight = (int) Math.round(height * sin + width * cos);

        BufferedImage rotatedImage = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_BGR);
        Graphics2D graphics = rotatedImage.createGraphics();

        graphics.translate((newWidth - width) / 2, (newHeight - height) / 2);
        graphics.rotate(radians, width / 2, height / 2);
        graphics.drawRenderedImage(image, null);
        graphics.dispose();

        return rotatedImage;
    }
}

 

3. Java 보조 Stream

• 기존 기반 Stream 문자열 지원
• 기존 기반 Stream 성능 개선
• 기존 메소드를 사용하기 간편하게 개선

 

• InputStreamReader

import java.io.IOException;
import java.io.InputStreamReader;

public class InputStreamReaderTest {
    public static void main(String[] args) {
        //InputStreamReader로 개선, 바이트 단위가 아니고 문자열 단위로 읽어들임
        int j = 0;
        StringBuilder sb1 = new StringBuilder();
        System.out.print("입력하세요 : ");
        try (InputStreamReader isr = new InputStreamReader(System.in)) {
            while ((j = isr.read()) != '\n') {
                sb1.append((char) j);
            }
            System.out.println(sb1);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

 

• BufferedReader / BufferedWriter

import java.io.*;

public class BufferedStreamTest {
    public static void main(String[] args) {
        try (FileReader fr = new FileReader("src/exercise/chapter_56/test_long.txt");
             FileWriter fw = new FileWriter("src/exercise/chapter_56/output_test_long.txt")) {

            long start = System.currentTimeMillis();
            int data;
            while ((data = fr.read()) != -1) {
                fw.write((char) data);
            }
            long end = System.currentTimeMillis();
            System.out.println("Buffered 적용 전 : " + (end - start) + "ms");
        } catch (FileNotFoundException e) {
            throw new RuntimeException(e);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

        //BufferedReader/Writer로 개선
        try (BufferedReader br = new BufferedReader(new FileReader("src/exercise/chapter_56/test_long.txt"));
             BufferedWriter bw = new BufferedWriter(new FileWriter("src/exercise/chapter_56/bufferd_output_long.txt"))
        ) {
            long start = System.currentTimeMillis();
            int data;
            while ((data = br.read()) != -1) {
                bw.write((char) data);
            }
            long end = System.currentTimeMillis();
            System.out.println("Buffered 적용 전 : " + (end - start) + "ms");
        } catch (FileNotFoundException e) {
            throw new RuntimeException(e);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

 

• PrintWriter로 개선

import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

public class PrintWriterTest {
    public static void main(String[] args) {
        String fileName = "src/exercise/chapter_56/output.txt";
        try (FileWriter fileWriter = new FileWriter(fileName)) {
            fileWriter.write("FileWriter Example\n");

            int num = 42;
            String formattedNumber = String.format("정수형 format %d\n", num);
            fileWriter.write(formattedNumber);

            double value = 3.14;
            String formattedValue = String.format("실수형 format %.2f", value);
            fileWriter.write(formattedValue);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

        //PrintWriter로 개선, pritnln, printf 등 사용 가능
        fileName = "src/exercise/chapter_56/output2.txt";
        try (PrintWriter printWriter = new PrintWriter(fileName)) {
            printWriter.println("FileWriter Example"); 

            int num = 42;
            printWriter.printf("정수형 format %d\n", num);

            double value = 3.14;
            printWriter.printf("실수형 format %.2f", value);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

 

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