> 原文：[https://www.geeksforgeeks.org/java-program-to-print-all-duplicate-characters-in-a-string/](https://www.geeksforgeeks.org/java-program-to-print-all ...

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Follow these steps to find ... String variable to a non-null value Call the Java String length() method Hold the value of the String length in a variable for future use The Java String class contains ...