ããã ããGuavaã£ã¦ã©ã¤ãã©ãªãè¯ãã£ã¦ã¤ã³ã¿ã¼ãããã«æ¸ãã¦ãã®ã§èª¿ã¹ã¦ã¿ããã ãµã³ãã«ã½ã¼ã¹ã®ã»ã¨ãã©ã¯æ¬å®¶ããã³ãããããã guava-libraries - Guava: Google Core Libraries for Java 1.6+ - Google Project Hosting Basic Using/avoiding null nullã½ãé¿ããããã®ä»çµã¿ {% highlight java %} Optional possible = Optional.of(5); possible.isPresent(); // returns true possible.get(); // returns 5 Preconditions å¼æ°ã®å¤ãã§ãã¯ãªã©ãåææ¡ä»¶ããã§ãã¯ããä»çµã¿ãassertã¨ãã«ä¼¼ã¦ãã¨æãã æ¡ä»¶ãfalseã ã¨å¯¾å¿ããExceptio
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