The function and purpose of the "Core" framework in the Java class library
The function and purpose of the "Core" framework in the Java class library
Java Standard Library provides a module called "Core" framework, which contains a set of basic classes and interfaces, providing developers with many important functions and tools.These functions and uses cover all aspects of Java programming, including string processing, collective operations, files and IO operations, date and time processing, and so on.The following will introduce several common functions of the "Core" framework.
1. String processing: Java's Core library provides some commonly used string processing tool classes, such as String class and StringBuilder classes.The String class provides a series of methods to perform common operations on string, such as obtaining the length of the strings, connecting string, extracting subcumbers, comparative string, etc.The StringBuilder class provides high -efficiency string stitching and modification functions, which is suitable for frequent operating string scenarios.
Example code:
String str = "Hello";
str = str.concat ("world"); // string stitching
System.out.println (str); // Output: Hello World
StringBuilder builder = new StringBuilder();
builder.append("Hello");
builder.append(" ");
builder.append("World");
String result = builder.tostring (); // Convert to a string
System.out.println (result); // Output: Hello World
2. Collective operation: The Core library of Java provides a series of collection classes and interfaces, such as List, SET, MAP, etc., for various collection operations.These collection classes have different characteristics and uses, and can choose suitable collection types according to actual needs.Through the collection class, developers can easily perform operations such as addition, deletion, change, and other operations.
Example code:
List<String> list = new ArrayList<>();
list.add("Apple");
list.add("Banana");
list.add("Orange");
System.out.println (list); // Output: [Apple, Banana, Orange]
list.remove("Banana");
System.out.println (list); // Output: [Apple, Orange]
Map<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
3. File and IO operation: Core library provides some classes and interfaces to process files and input and output operations, such as File class, inputStream, and OutputStream classes.Through these classes, you can read and write files to realize the operation of file copying, movement, deletion, etc.
Example code:
File file = new File("test.txt");
try {
FileWriter writer = new FileWriter(file);
writer.write("Hello World");
writer.close();
FileReader reader = new FileReader(file);
int data;
while ((data = reader.read()) != -1) {
System.out.print((char) data);
}
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
4. Date and time processing: The Core library of Java provides some classes and interfaces for processing date and time -related operations.Among them, the most commonly used classes are Date and CALENDAR classes. They provide various methods to analyze and format the date, calculation time difference, and adjustment date.
Example code:
Date date = new Date();
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateString = format.format(date);
System.out.println (datestring); // Output: The current date and time
Calendar calendar = Calendar.getInstance();
int year = calendar.get(Calendar.YEAR);
int month = calendar.get(Calendar.MONTH) + 1;
int day = calendar.get(Calendar.DAY_OF_MONTH);
System.out.printf("%d-%d-%d
", year, month, day); // Output: The current date
In short, the "Core" framework of the Core library of Java provides many important functions and tools, and provides rich class and interfaces for programming requirements for string processing, collective operations, files and IO operations, date and time processingEssenceDevelopers can choose suitable functions and tools according to actual needs to improve development efficiency.
