Java运行时类

用于与Java运行时环境交互的类在Java中称为运行时类，它提供了Runtime.getRuntime()、exit(int status)、addShutdownHook(Thread hook)、Process exec( String命令）抛出输入输出异常，availableProcessors()、freeMemory()、totalMemory()等，用于进程执行、调用GC、获取总内存、获取空闲内存等，声明为public class Runtime 扩展了对象，并且只有一个 Java 应用程序只能使用 java.lang.Runtime 类的一个实例，并且使用 Java 中的 Runtime.getRuntime() 方法返回 Runtime 类的单例实例。

Java Runtime 类的方法

Java运行时类有多种方法。他们是：

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1.运行时 getRuntime()

使用 Runtime getRuntime() 方法返回 Run time 类的实例。考虑下面的 Java 程序来演示 Java 运行时类的 Runtime getRuntime() 方法。

代码：

//a class called program is defined
public class program
{
//main method is called
public static void main(String[] args)
{
// The current runtime in association with process is obtained using getRuntime method.
Runtime roll = Runtime.getRuntime();
// The current free memory for the current runtime is obtained using freeMemory() method.
System.out.println("The current free memory for the current runtime is" + roll.freeMemory());
}
}

输出：

         

说明：在上面的程序中，定义了一个名为program的类。然后调用main方法。然后使用 getRuntime 方法获取与进程关联的当前运行时间。然后使用 freeMemory() 方法获取当前运行时的当前可用内存。

2.退出（int状态）

使用 Runtime exit(int status) 方法终止当前虚拟机。考虑下面的 Java 程序来演示 Java 运行时类的 exit(int status) 方法。

代码：

//a class called program is defined
public class program
{
//main method is called
public static void main(String[] args)
{
//the current runtime or program is caused to exit using exit(int status) method
Runtime.getRuntime().exit(0);
//This statement is not executed because the program is terminated by the usage of exit(int status) method above
System.out.println("Checking if the program executes this statement depsite the use of exit(int status) method");
}
}

输出：

        

上述程序的输出是空白的。

说明：在上面的程序中，定义了一个名为program的类。然后调用main方法。然后使用 exit(int status) 方法导致当前运行时或程序退出。那么该语句就不会被执行，因为程序被上面语句中的 exit(int status) 方法终止了。

3. addShutdownHook(线程钩子)

使用addShutdownHook(Thread Hook)方法注册一个新的钩子线程。考虑下面的 Java 程序来演示 Java 运行时类的 addShutdownHook(Thread Hook) 方法。

代码：

//a class called program is defined
public class program
{
// when the program is about to exit, this class extending the thread is called
static class Mess extends Thread
{
public void run()
{
System.out.println("The program is going to exit");
}
}
//main method is called
public static void main(String[] args)
{
try
{
//the class mess is registered as shut down hook
Runtime.getRuntime().addShutdownHook(new Mess());
//The thread is made to sleep for certain seconds
System.out.println("Five seconds of waiting time for the program to exit");
Thread.sleep(5);
}
catch (Exception ex)
{
ex.printStackTrace();
}
}
}

输出：

说明：在上面的程序中，定义了一个名为program的类。当程序即将退出时，会调用这个扩展线程的类。然后调用main方法。然后类混乱被注册为关闭钩子。然后线程会休眠几秒钟。

4.进程 exec(String command) 抛出 IOException

给定的命令是使用 Process exec(String command) throws IOException 方法在单独的进程中执行的。考虑下面的 Java 程序来演示 Process exec(String command) throws IOExceptionmethod of Java Run time class

代码：

//a class called program is defined
public class program
{
//main method is called
public static void main(String[] args)
{
try
{
// a process is created to execute google chrome
Process proc = Runtime.getRuntime().exec("google-chrome");
System.out.println("Successfully started google chrome");
}
catch (Exception e)
{
e.printStackTrace();
}
}
}

输出：

说明：在上面的程序中，定义了一个名为program的类。然后调用main方法。然后创建一个进程来执行google chrome。

5.可用处理器()

可用处理器的数量使用 availableProcesors() 方法返回。考虑下面的 Java 程序来演示 Java 运行时类的 availableProcessors() 方法。

代码：

//a class called program is defined
public class program
{
//main method is called
public static void main(String[] args)
{
//checking for the number of available processors using availableprocessors() method.
System.out.println("The number of available processors are " + Runtime.getRuntime().availableProcessors());
}
}

输出：

说明：在上面的程序中，定义了一个名为program的类。然后调用main方法。然后使用 availableprocessors() 方法检查可用处理器的数量。

6.释放内存()

使用 freeMemory() 方法在 JVM 中返回可用内存量。

考虑下面的 Java 程序来演示 Java 运行时类的 freeMemory() 方法。

代码：

//a class called program is defined
public class program
{
//main method is called
public static void main(String[] args)
{
//The amount of free memory available is given by using freememory() method
System.out.println("The amount of free memory available is " + Runtime.getRuntime().freeMemory());
}
}

输出：

Explanation: In the above program, a class called program is defined. Then the main method is called. Then the amount of free memory available is given by using freememory() method.

7. totalMemory()

The amount of total memory is returned in JVM using totalMemory()method. Consider the below Java program to demonstrate totalMemory() method of the Java Run time class.

Code:

//a class called program is defined
public class program
{
//main method is called
public static void main(String[] args)
{
//The amount of total memory available is given by using totalmemory() method
System.out.println("The amount of free memory available is " + Runtime.getRuntime().totalMemory());
}
}

Output:

Explanation: In the above program, a class called program is defined. Then the main method is called. Then the amount of total memory available is given by using totalmemory() method.

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