Java 初始化时定义一个不可改变的Map集合

    xiaoxiao2022-07-12  163

    初始化时定义一个不可改变的Map集合

    代码

    package com.zhaohp.sofaboot; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.boot.test.context.SpringBootTest; import org.springframework.test.context.junit4.SpringRunner; import java.util.Collections; import java.util.HashMap; import java.util.Map; @RunWith(SpringRunner.class) @SpringBootTest(classes = SofabootApplication.class, webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT) public class SofabootApplicationTests { private static Map<Integer, String> map = new HashMap<Integer, String>(); static { map.put(1, "one"); map.put(2, "two"); map = Collections.unmodifiableMap(map); } @Test public void test1() { try { map.put(1, "three"); } catch (UnsupportedOperationException e) { System.out.println("This Map cannot be modified."); e.printStackTrace(); } } }

    异常

    java.lang.UnsupportedOperationException

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