获得JVM的总内存，最大内存，以及空闲内存

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();
    }
}