Common in Java class libraries

Common Knowledge Articles in Java Class Libraries Java is a widely used programming language with rich class libraries and tools that can help developers complete various tasks more efficiently. In the Java class library, there are many common classes and methods that can be used to handle various requirements. Here are some common Java class libraries and their purposes. 1. Java. lang. String class: This class is one of the most commonly used classes in Java. It provides many methods for handling strings, such as concatenation, segmentation, substitution, truncation, and so on. Here is an example code: String str = "Hello, World!"; String newStr = str.replace("Hello", "Hi"); System. out. println (newStr)// Output: Hi, World! 2. Java. util. ArrayList class: This class implements an resizable array for storing objects. It provides a series of commonly used methods, such as adding, deleting, obtaining, traversing, and so on. Here is an example code: ArrayList<String> list = new ArrayList<>(); list.add("apple"); list.add("banana"); list.add("orange"); System. out. println (list. get (1))// Output: banana 3. Java. util. HashMap class: This class implements a hash map for storing key value pairs. It provides a series of commonly used methods, such as adding, deleting, obtaining, traversing, and so on. Here is an example code: HashMap<String, Integer> map = new HashMap<>(); map.put("apple", 1); map.put("banana", 2); map.put("orange", 3); System. out. println (map. get ("banana"))// Output: 2 4. Java. util. Date class: This class is used to represent dates and times. It provides some commonly used methods, such as obtaining the current time, formatting dates, and so on. Here is an example code: Date now = new Date(); SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); String formattedDate = format.format(now); System. out. println (formatedDate)// Output: Formatted string for the current time 5. Java. io. File class: This class is used to represent file and directory paths. It provides some commonly used methods, such as creating files, deleting files, renaming files, and so on. Here is an example code: File file = new File("test.txt"); if (file.exists()) { System. out. println ("file exists"); } else { System. out. println ("file does not exist"); } This is just a small subset of common classes and methods in Java class libraries. The Java class library is very large, and there are many other classes that can be used for various tasks. By utilizing Java class libraries well, developers can more efficiently complete various programming tasks.