Map的key和value是否允許null？

直接寫程序驗證一下：

import java.util.HashMap; import java.util.Hashtable; import java.util.Map; import java.util.TreeMap; import java.util.concurrent.ConcurrentHashMap;/*** @author robin*/ public class MyTest {public static void main(String[] args) {Map<Object, Object> m1 = new HashMap<>();Map<Object, Object> m2 = new TreeMap<>();Map<Object, Object> m3 = new Hashtable<>();Map<Object, Object> m4 = new ConcurrentHashMap<>();try {m1.put("zzz", null);} catch (Exception e) {System.out.println("m1-a：" + e.getMessage());}try {m1.put(null, null);} catch (Exception e) {System.out.println("m1-b：" + e.getMessage());}try {m2.put("zzz", null);} catch (Exception e) {System.out.println("m2-a：" + e.getMessage());}try {m2.put(null, null);} catch (Exception e) {System.out.println("m2-b：" + e.getMessage());}try {m3.put("zzz", null);} catch (Exception e) {System.out.println("m3-a：" + e.getMessage());}try {m3.put(null, null);} catch (Exception e) {System.out.println("m3-b：" + e.getMessage());}try {m4.put("zzz", null);} catch (Exception e) {System.out.println("m4-a：" + e.getMessage());}try {m4.put(null, null);} catch (Exception e) {System.out.println("m4-b：" + e.getMessage());}}}

執(zhí)行結果：

?

m2-b：null m3-a：null m3-b：null m4-a：null m4-b：null

結論如下表：

轉載于:https://www.cnblogs.com/amunote/p/10211760.html

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