ラムダ式とStreamAPI

ラムダ式

関数を生み出し、即時利用

public class Main {

	public static void main(String[] args) {
		double b = 3.14;
		IntToDoubleFunction func = x -> {
			x = 3;
			return x * x * b;
		};
		
		Function <String, Integer> func1 = (String s) ->{
			return s.length();};
			int num = func1.apply("ABCD");
			System.out.println("ABCDは" + num + "文字です。");
	}
}

並び替え

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

public class Main6 {
	public static void main(String[] args) {
		List<Account> list = new ArrayList<>();
		list.add(new Account(800,"Saving"));
		list.add(new Account(600,"Check"));
			
		
		list.sort((a, b) -> (a.balanceX - b.balanceX));
		list.forEach(account -> System.out.println(account.balanceX + " " + account.accountNo));
	}
}

public class Account {
	int balanceX;
	String accountNo;
	
	Account(int balanceX, String accountNo){
		this.balanceX = balanceX;
		this.accountNo = accountNo;
	}
}

StreamAPI

リストとして取り出す

import java.util.List;

public class Main5 {

	public static void main(String[] args) {
		List<String> names = List.of("Smith", "Mike", "Keisuke", "Chen");
		names.stream().filter(n -> n.length() <= 5).map(n -> n + "さん").forEach(System.out::println);
	}

}

条件に合うデータだけを抽出

import java.util.ArrayList;

public class Main7 {

	public static void main(String[] args) {
		ArrayList<Human> list = new ArrayList<>();

		list.add(new Human("Alice", 100));
		list.add(new Human("Keisuke", 300));
		list.add(new Human("Mark", 400));
		list.add(new Human("Sara", 50));

		boolean flg = false;

		flg = list.stream().anyMatch(h -> h.getHp()>100);
		System.out.println(flg);

	}
}

参考資料

スッキリわかるJava入門 実践編 第3版 (スッキリわかる入門シリーズ)