JDK source code analysis-Runtime class

The Runtime class is the singleton design pattern used

Through the source code to see which singleton mode is used

public class Runtime {
    private static Runtime currentRuntime = new Runtime();
​
    /**
     * Returns the runtime object associated with the current Java application.
     * Most of the methods of class <code>Runtime</code> are instance
     * methods and must be invoked with respect to the current runtime object.
     *
     * @return  the <code>Runtime</code> object associated with the current
     *          Java application.
     */
    public static Runtime getRuntime() {
        return currentRuntime;
    }
​
    /** Don't let anyone else instantiate this class */
    private Runtime() {}
    ...
}

It can be seen from the above source code that the Runtime class uses the hungry Chinese (static attribute) method to implement the singleton mode.

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Use the methods in the Runtime class

public class RuntimeDemo {
    public static void main(String[] args) throws IOException {
        //获取Runtime类对象
        Runtime runtime = Runtime.getRuntime();
​
        //返回 Java 虚拟机中的内存总量。
        System.out.println(runtime.totalMemory());
        //返回 Java 虚拟机试图使用的最大内存量。
        System.out.println(runtime.maxMemory());
​
        //创建一个新的进程执行指定的字符串命令，返回进程对象
        Process process = runtime.exec("ipconfig");
        //获取命令执行后的结果，通过输入流获取
        InputStream inputStream = process.getInputStream();
        byte[] arr = new byte[1024 * 1024* 100];
        int b = inputStream.read(arr);
        System.out.println(new String(arr,0,b,"gbk"));
    }
}