查看JVM内存情况

package cn.dsna.common.java;

import java.lang.Runtime;
/**
 * 查看JVM内存大小
 * @author DSNA
 * @date 2010-04-21
 */
public class JVMMemory {
	public static void main(String args[]) {
		System.out.println(new JVMMemory());
	}

	/**
	 * 已占用内存
	 * 
	 * @return
	 */
	public long totalMemory() {
		long l = Runtime.getRuntime().totalMemory();
		return (l / 1024 / 1024);
	}

	/**
	 * 分配最大内存
	 * 
	 * @return
	 */
	public long maxMemory() {
		long l = Runtime.getRuntime().maxMemory();
		return (l / 1024 / 1024);
	}

	/**
	 * 空余内存
	 * @return
	 */
	public long freeMemory() {
		long l = Runtime.getRuntime().freeMemory();
		return (l / 1024 / 1024);
	}
	
	public String toString(){

		long t = totalMemory();
		long fr = freeMemory();
		long max = maxMemory();
		long rem = t - fr;
		StringBuilder sb=new StringBuilder();
		sb
		.append("最大内存:" + max + " MB\n")
		.append("占用系统内存:" + t + " MB\n")
		.append("实际占用内存:" + rem + " MB\n")
		.append("剩余内存:" + fr + " MB\n");
		return sb.toString();
	}
}

// 改变JVM内存大小的方法
// java -Xms100m -Xmx250 JVMMemory
//eclipse设置jvm arg Run>run config.... (x)- >jvm -arg.......
// -Xmx1024M -Xms512M -XX:MaxPermSize=256m