關於HashMap的一個有趣的小程序

import java.util.*;

public class TestArgsWords {
	private static final Integer ONE = new Integer(1);
	
	public static void main(String[] args) {
		Map<String, Integer> m = new HashMap<>();
		for (int i = 0; i < args.length; i++) {
			Integer freq = m.get(args[i]);
			m.put(args[i], freq == null ? ONE : new Integer(freq.intValue() + 1));
		}
		System.out.println(
				m.size() + " distinct words detected:");
		System.out.println(m);
	}
}

或者利用 auto_boxing / auto_unboxing 機制寫成：

import java.util.*;

public class TestArgsWords {
	private static final int ONE = 1;
	
	public static void main(String[] args) {
		Map<String, Integer> m = new HashMap<>();
		for (int i = 0; i < args.length; i++) {
			int freq = m.get(args[i]) == null ? 0 : m.get(args[i]);
			m.put(args[i], freq == 0 ? ONE : freq + 1);
		}
		System.out.println(
				m.size() + " distinct words detected:");
		System.out.println(m);
	}
}

運行結果：