獲得JVM的總內存，最大內存，以及空閑內存

要獲得jvm相關的內存信息，需要使用Runtime類的totalMemory(), maxMemory() 和 freeMemory()方法。

import java.text.DecimalFormat;

/**

Main.java
*/
public class Main {
/**

Displays the total amount of memory, the maximal amount of memory
and the total amount of free memory in the Java Virtual Machine.
*/
public void displayAvailableMemory() {
DecimalFormat df = new DecimalFormat("0.00") ;
//Display the total amount of memory in the Java virtual machine.
 long totalMem = Runtime.getRuntime().totalMemory();
System.out.println(df.format(totalMem 1000000F) + " MB");
//Display the maximum amount of memory that the Java virtual machine will attempt to use.
 long maxMem = Runtime.getRuntime().maxMemory();
 System.out.println(df.format(maxMem 1000000F) + " MB");
//Display the amount of free memory in the Java Virtual Machine.
 long freeMem = Runtime.getRuntime().freeMemory();
 System.out.println(df.format(freeMem 1000000F) + " MB");
}
/**

Starts the program
*
@param args the command line arguments
*/
public static void main(String[] args) {
 new Main().displayAvailableMemory();
}
}</pre>