1월 26일(목) - 7장(자바 날개 달기)

7장 - 자바 날개 달기(7-4, 7-5, 7-6)

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7-4 예외처리

1) finally

// 7-4 finally
public class Sample{
    public void shouldBeRun(){
        System.out.println("ok thanks.");
    }

    public static void main(String[] args){
        Sample sample =  new Sample();
        int c;
        try {
            c = 4 / 0;
            //sample.shouldBeRun();
        }catch (ArithmeticException e){
            c = -1;
        } finally{
            sample.shouldBeRun();
        }
    }
}

2) RuntimeException과 Exception

//7-4 RuntimeException 과 Exception
class FoolException extends Exception{

}
public class Sample{
    public void sayNick(String nick){
        try {
            if ("fool".equals(nick)) {
                throw new FoolException();
            }
            System.out.println("당신의 별명은 " + nick + " 입니다.");
        }catch(FoolException e){
            System.err.println("FoolException이 발생했습니다.");
        }
    }
    public static void main(String[] args){
        Sample sample = new Sample();
        sample.sayNick("fool");
        sample.sayNick("genious");
    }
}

3)

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7-5 쓰레드

1) Thread

//7-5 Thread
public class Sample extends Thread{
    int seq;

    public Sample(int seq){
        this.seq = seq;
    }
    public void run(){
        System.out.println(this.seq + " thread start.");
        try{
            Thread.sleep(1000);
        }catch (Exception e){
        }
        System.out.println(this.seq + " thread end");
    }
    public static void main(String[] args){
        for(int i=0; i<10; i++){
            Thread t = new Sample(i);
            t.start();
        }
        System.out.println("main end.");
    }
}

2) Join

//7-5 Join
import java.util.ArrayList;
public class Sample extends Thread{
    int seq;

    public Sample(int seq){
        this.seq = seq;
    }
    public void run(){
        System.out.println(this.seq + " thread start.");
        try{
            Thread.sleep(1000);
        }catch (Exception e){
        }
        System.out.println(this.seq + " thread end");
    }
    public static void main(String[] args){
        ArrayList<Thread> threads = new ArrayList<>();
        for(int i=0; i<10; i++){
            Thread t = new Sample(i);
            t.start();
            threads.add(t);
        }
        for(int i=0; i<threads.size(); i++){
            Thread t = threads.get(i);
            try{
                t.join();
            }catch (Exception e){
            }
        }

        System.out.println("main end.");
    }
}

3) Runnable

//7-5 Runnable
import java.util.ArrayList;
import java.util.concurrent.TransferQueue;

public class Sample implements Runnable{
    int seq;

    public Sample(int seq){
        this.seq = seq;
    }
    public void run(){
        System.out.println(this.seq + " thread start.");
        try{
            Thread.sleep(1000);
        }catch (Exception e){
        }
        System.out.println(this.seq + " thread end");
    }
    public static void main(String[] args){
        ArrayList<Thread> threads = new ArrayList<>();
        for(int i=0; i<10; i++){
            Thread t = new Thread(new Sample(i));
            t.start();
            threads.add(t);
        }
        for(int i=0; i<threads.size(); i++){
            Thread t = threads.get(i);
            try{
                t.join();
            }catch (Exception e){
            }
        }

        System.out.println("main end.");
    }
}

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7-6 함수형 프로그래밍

1) Lambda

// 7-6 함수형 프로그래밍 - Lambda
@FunctionalInterface
interface Calculator{
    int sum(int a, int b);
}
public class Sample{
    public static void main(String[] args){
        Calculator mc = (int a, int b) -> a +b;
        int result = mc.sum(3,4);
        System.out.println(result);
    }
}

2) Stream

// 7-6 Stream 적용 전
import java.util.Arrays;
import java.util.Comparator;

public class Sample{
    public static void main(String[] args){
        int[] data = {5, 6, 4, 2, 3, 1, 1, 2, 2, 4, 8};
        int[] result = Arrays.stream(data)
                .boxed()
                .filter((a) -> a%2 == 0)
                .distinct()
                .sorted(Comparator.reverseOrder())
                .mapToInt(Integer::intValue)
                .toArray()
                ;
    }
}

// 7-6 Stream 적용 후
import java.util.*;

public class Sample{
    public static void main(String[] args){
        int[] data = {5, 6, 4, 2, 3, 1, 1, 2, 2, 4, 8};

        ArrayList<Integer> dataList = new ArrayList<>();
        for(int i=0; i<data.length; i++){
            if(data[i] % 2 == 0){
                dataList.add(data[i]);
            }
        }

        HashSet<Integer> dataSet = new HashSet<>(dataList);
        ArrayList<Integer> distinctList = new ArrayList<>(dataSet);
        distinctList.sort(Comparator.reverseOrder());
        int[] result = new int[distinctList.size()];
        for(int i=0; i< distinctList.size(); i++){
            result[i] = distinctList.get(i);
        }
    }
}

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