[Java 실습] 5. 자바 중급 활용

Q1. 예외처리 기본

package com.dinfree;

import java.io.File;
import java.util.Scanner;

public class ExceptionTest1001 {
	public static void main(String[] args) {
		File file=new File("test.txt");
		Scanner scan;
		scan = new Scanner(file);
		while(scan.hasNext()) {
			System.out.println(scan.next());
		}
	}

}

 

package com.dinfree;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class ExceptionTest1001 {
	public static void main(String[] args) {
		File file=new File("test.txt");
		Scanner scan;
		try {
			scan = new Scanner(file);
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		
	}

	}
}

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Q2. 사용자 예외 클래스 구현

 

package com.dinfree;

public class ExceptionTest2_1001 extends Exception{
	String exMsg;
	
	public ExceptionTest2_1001(String msg)
	{
		exMsg = "ExceptionTest : "+msg;
	}
	
	@Override
	public String getMessage() {
		return exMsg;
	}

}

 

package com.dinfree;

public class ExceptionTest3_1001 {
	int num;
	
	public void doException() throws ExceptionTest2_1001{
		if(num==1)
			System.out.println("OK");
		else
			throw new ExceptionTest2_1001("doException");
	}
	
	public static void main(String[] args) {
		ExceptionTest3_1001 app = new ExceptionTest3_1001();
		app.num=2;
		try {
			app.doException();
			
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

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Q3. 자바 문자열 생성과 비교

 

package com.dinfree_1001;

public class StringTest1 {
	public static void main(String[] args) {
		String s1=new String("hello");
		String s2="hello";
		
		System.out.printf("%s, %s\n", s1.hashCode(), s2.hashCode());
		
		String s3=new String("hello");
		String s4="hello";
		
		System.out.printf("%s, %s\n", s3.hashCode(), s4.hashCode());
		
		System.out.printf("s1==s2: %s\n", s1==s2);
		System.out.printf("s1==s3: %s\n", s1==s3);
		System.out.printf("s2==s4: %s\n", s2==s4);
		System.out.printf("s1.equals(s2): %s\n", s1.equals(s2));
		
		s2 = s2+ " world";
		String s5 = "hello world";
		
		System.out.printf("s2==s5:%s\n", s2==s5);
	}
	

}

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Q4. 문자열 처리

 

package com.dinfree_1001;

import java.util.Arrays;
import java.util.StringJoiner;

public class StringTest2 {
	public static void main(String[] args) {
		StringJoiner sj = new StringJoiner(",", "[", "]");
		String[] carArr= { "hyunadi", "mercedes", "bmw"};
		
		for(String s : carArr)
		{
			sj.add(s.toUpperCase());
		}
		System.out.println(sj.toString());
		
		String s1 = " Hello World   ";
		String s2 = s1.trim();
		System.out.printf("#%s#\n", s1);
		System.out.printf("#%s#\n", s2);
		
		String s3=s1.substring(1,3);
		System.out.println(s3);
		
		System.out.println(s1.replace('l', 'k'));
		
		char[] carr=s2.toCharArray();
		System.out.println(Arrays.toString(carr));
	}

}

 

package com.dinfree_1001;

public class StringTest3 {
	public static void main(String[] args) {
		String s1="Hello World";
		System.out.println(s1);
		System.out.printf("indexOf('l'): %s\n", s1.indexOf('l'));
		System.out.printf("lastIndexOf('l'): %s\n", s1.lastIndexOf('l'));
		System.out.printf("charAt(6) : %s\n", s1.charAt(6));
		System.out.printf("startWith(\"He\"): %s\n", s1.startsWith("He"));
		System.out.printf("length(): %s\n", s1.length());
		
		StringBuffer sb = new StringBuffer();
		sb.append("Hello");
		sb.append(" World");
		
		String str=sb.toString();
		System.out.println(str);
	}

}

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Q5. 날짜 시간 구하기 기본

 

package com.dinfree_1001;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;

public class DateTimeTest1 {
	public static void main(String[] args) {
		LocalDate d1 = LocalDate.now();
		LocalDate d2 = LocalDate.of(2019, 10, 10);
		
		LocalTime t1=LocalTime.now();
		LocalTime t2=LocalTime.of(7, 20, 20);
		
		System.out.printf("LocalDate.now() : %s\n", d1);
		System.out.printf("LocalDate.of(2019, 10, 10): %s\n", d2);
		System.out.printf("LocalTime t1=LocalTime.now() : %s\n", t1);
		System.out.printf("LocalTime.of(7, 20, 20) : %s\n", t2);
		
		LocalDateTime dt1=LocalDate.now().atTime(LocalTime.MIDNIGHT);
		LocalDateTime dt2=LocalDate.now().atTime(LocalTime.MAX);
		
		System.out.printf("LocalDate.now().atTime(LocalTime.MIDNIGHT) : %s\n", dt1);
		System.out.printf("LocalDate.now().atTime(LocalTime.MAX) : %s\n", dt2);
	}

}

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Q6. 날짜 형식 지정 및 시간차이 계산

package com.dinfree_1001;

import java.time.Duration;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.Period;
import java.time.format.DateTimeFormatter;
import java.time.format.FormatStyle;

public class DateTimeTest2 {
	public static void main(String[] args) {
		LocalDateTime dt1=LocalDateTime.now();
		DateTimeFormatter dtf=DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT);
		
		System.out.println(dtf.format(dt1));
		System.out.println(dt1.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
		
		System.out.println(dt1.plusDays(2));
		System.out.println(LocalTime.now().minusHours(3));
		System.out.println(Duration.ofMinutes(10).getSeconds());
		
		LocalTime start=LocalTime.of(11, 40, 50);
		LocalTime end = LocalTime.of(11, 42, 50);
		
		Duration duration = Duration.between(start, end);
		
		System.out.println("Seconds : "+duration.getSeconds());
		
		LocalDate startDate = LocalDate.of(1950, 9, 1);
		LocalDate endDate = LocalDate.of(2010, 9, 2);
		Period period = Period.between(startDate, endDate);
		
		System.out.println("Years : "+period.getYears());
		System.out.println("Months : "+period.getMonths());
		System.out.println("Days : "+period.getDays());
		
	}

}

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Q7. 기본적인 제네릭 클래스 생성과 사용

package com.dinfree_1001;

class StorageT1<T> {
	T item;
	
public T getItem() {
	return item;
}

public void setItem(T item) {
	this.item=item;
}
}

package com.dinfree_1001;

public class GenericsTest1 {

	public static void main(String[] args) {
		StorageT1<String> storage1=new StorageT1<>();
		storage1.setItem("MyItem");
		System.out.println(storage1.getItem());
		
		StorageT1<Integer> storage2=new StorageT1<>();
		storage2.setItem(20211001);
		System.out.println(storage2.getItem());
		

	}

}

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Q8. 제네릭 메서드 및 와일드 카드 사용 예제

package com.dinfree_1001;

import java.util.ArrayList;
import java.util.List;

public class GenericsTest2 {
	public <T> List<Character> convert(StorageT1<T> storage){
		ArrayList<Character> list = new ArrayList<>();
		
		String s = String.valueOf(storage.getItem());
		int size= s.length();
		for(int i=0; i<size; i++) {
			list.add(s.charAt(i));
		}
		return list;
	}
	public static void main(String[] args) {
		StorageT1<String> s1=new StorageT1<>();
		s1.setItem("MyItem");
		
		StorageT1<Integer> s2=new StorageT1<>();
		s2.setItem(20211001);
		
		GenericsTest2 gt2=new GenericsTest2();
		
		System.out.println(gt2.convert(s1));
		System.out.println(gt2.convert(s2));
		
		
	}

}

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