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import java.util.HashMap; public class Main { public static void main(String[] args) { HashMap<String, String> capitalCities = new HashMap<String, String>(); capitalCities.put("England", "London"); capitalCities.put("Germany", "Berlin"); capitalCities.put("Norway", "Oslo"); capitalCities.put("USA", "Washington DC"); // Add new entries only if they don't exist capitalCities.putIfAbsent("Canada", "Ottawa"); capitalCities.putIfAbsent("England", "Cambridge"); System.out.println(capitalCities); } }
{加拿大=渥太華, 美國=華盛頓哥倫比亞特區, 挪威=奧斯陸, 英國=倫敦, 德國=柏林}