What is the basic class library in java?

The basic class library is a class library provided by java. When we develop, we can select classes from the library and call its methods to implement some functions.

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For example:

(1) Scanner

Scanner can read user keyboard input and file input.

//System.in代表键盘输入
Scanner sc=new Scanner(System.in);
//增加下面一行将只把回车作为分隔符
sc.useDelimiter("\n");
//判断是否还有下一个输入项
while(sc.hasNext())
{
   //输出输入项
   System.out.println("键盘输入的内容是："+sc.next());
}

(2) System

The methods in the System class are:

1. Access the environment variables and system properties of the platform where the program is located;

2. Get the current time of the system - currentTimeMillis(), nanoTime();

3. in, out, and err represent the standard input, standard output, and error output streams of the system respectively;

4. It can return the exact hashCode value of the specified object. If the identityHashCode value of two objects is the same, the two objects must be the same object - identityHashCode(Object x);

(3) Runtime

The methods in the Runtime class are:

1. Notify the system to perform garbage collection and clean up system resources - gc(), runFinalization()

2. Load files and dynamic link libraries - load(), loadLibrary()

3. Access JVM related information, such as the number of processors, memory information, etc. ——availableProcessors(), totalMemory()

4. Directly start a separate process to run the operating system

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