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配列の配列の要素数の総和を求めるメソッドをJava8のラムダ式を使わない場合と使った場合の2通りの方法で書いたプログラム。
package info.pandanote.test;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
public class CountElement {
public static void test1(Map<Integer,Set<Integer>> a) {
int count = 0;
for (Entry<Integer,Set<Integer>> e: a.entrySet()) {
count += e.getValue().size();
}
System.out.println(count);
return;
}
public static void test2(Map<Integer,Set<Integer>> a) {
System.out.println(a.entrySet().stream().mapToInt(e -> e.getValue().size()).sum());
}
public static void main(String args[]) {
Map<Integer,Set<Integer>> a = new HashMap<Integer,Set<Integer>>();
a.put(1,new HashSet<Integer>(Arrays.asList(1,2,3,4,5)));
a.put(2,new HashSet<Integer>(Arrays.asList(1,2)));
a.put(3,new HashSet<Integer>(Arrays.asList(1,2,6,7,8,9)));
test1(a);
test2(a);
return;
}
}
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