[jdk14.0.2] 基礎4

ArrayList

import java.util.*;

public class MyApp {

	public static void main(String[] args){

		List<Integer> sales = new ArrayList<>();

		sales.add(10);
		sales.add(20);
		sales.add(30);

		for (int i = 0; i < sales.size(); i++){
			System.out.println(sales.get(i));
		}

		sales.set(0, 100);
		sales.remove(2);

		for (Integer sale: sales){
			System.out.println(sale);
		}
	}
}

HashSet // 重複しない、順番が定まらない
L TreeSet, LinkedHashSet

public static void main(String[] args){

		// HashSet<Integer> = new HashSet<>();
		Set<Integer> sales = new HashSet<>();

		sales.add(10);
		sales.add(20);
		sales.add(30);
		sales.add(10);

		System.out.println(sales.size());
		for(Integer sale:sales){
			System.out.println(sale);
		}

		sales.remove(30);

		for(Integer sale:sales){
			System.out.println(sale);
		}
	}

HashMap

public class MyApp {

	public static void main(String[] args){
		// HashMap: key value
		// HashMap<String, Integer> sales = new HashMap<>();
		Map<String, Integer> sales = new HashMap<>();

		sales.put("tom", 10);
		sales.put("bob", 20);
		sales.put("steve", 30);

		System.out.println(sales.get("tom"));
		System.out.println(sales.size());

		for(Map.Entry<String, Integer> sale: sales.entrySet()){
			System.out.println(sale.getKey() + ":" + sale.getValue());
		}

		sales.put("tom", 100);
		sales.remove("steve");

		for(Map.Entry<String, Integer> sale: sales.entrySet()){
			System.out.println(sale.getKey() + ":" + sale.getValue());
		}
	}
}

StreamAPI

public static void main(String[] args){
		List<Integer> sales = new ArrayList<>(Arrays.asList(12, 30, 22, 4, 9));

		// for(Integer sale: sales){
		// 	System.out.println(sale);
		// }
		sales
			.stream()
			.filter(e-> e % 3 == 0)
			.map(e-> "(" + e + ")")
			.forEach(System.out::println);
		
	}

LocalDateTime class

import java.time.*;
import java.time.format.DateTimeFormatter;

public class MyApp {

	public static void main(String[] args){
		LocalDateTime d = LocalDateTime.now();

		System.out.println(d.getYear());
		System.out.println(d.getMonth().getValue());

		System.out.println(d.plusMonths(2).minusDays(3));

		DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy!MM!dd!");
		System.out.println(d.format(dtf));
	}
}