Overview and usage of the Core framework in the Java class library

Overview and usage of the Core framework in the Java class library The Java class library is an indispensable part of Java development, and the Core framework of the Java class library is the most basic and core part of the Java class library.It provides many commonly used classes and tools to support the development and execution of Java programs. The Core framework contains the basic class, interface and abnormal processing mechanism of Java, and also includes some commonly used tools, such as collection classes, date time classes, file operation classes, and so on.These classes and tools aim to provide a convenient and efficient programming method to help developers handle various common programming tasks. The following are examples and use methods commonly used in some Core frameworks: 1. String class: String class is one of the most commonly used categories in Java, which is used to process string.Here are some common methods of String class: String str = "Hello, World!"; System.out.println (str.tolowercase ()); // Output: Hello, World! System.out.println (str.length ()); // Output: 13 System.out.println (str.substring (7)); // Output: world! 2. ArrayList class: ArrayList is a dynamic array that can automatically adjust the capacity.The following is a common method for some ArrayList classes: ArrayList<String> list = new ArrayList<>(); list.add("Apple"); list.add("Banana"); list.add("Orange"); System.out.println (list.get (1)); // Output: banana System.out.println (list.size ()); // Output: 3 System.out.println (list.contains ("Apple"); // Output: TRUE 3. Date class: Date class is used to handle date and time.Here are some commonly used methods for Date class: Date date = new Date(); System.out.println (date); // Output: thu nov 25 12:00:00 cst 2021 DateFormat df = new SimpleDateFormat("yyyy-MM-dd"); System.out.println (df.format (date)); // Output: 2021-11-25 4. FILE class: The file class realizes the access to the file system and the directory.Here are some common methods for File class: File file = new File("test.txt"); System.out.println (file.exists ()); // Output: true System.out.println (file.isfile ()); // Output: true System.out.println (file.length ()); // Output: 1024 File dir = new File("path/to/dir"); System.out.println (dir.isdirectory ()); // Output: true System.out.println (dir.listFiles ()); // The file and subdirectory in the output directory By using the class and tools provided by the Core framework, we can develop the Java program more easily.These classes and tools provide rich functions and methods to greatly simplify our programming work.Whether it is processing string, collection operation, date and time processing or file operation, the Core framework provides corresponding classes and methods for us to use.Let's start with the Core framework, master the basic knowledge of Java, and lay a solid foundation for developing more complex applications.