System类的常用方法
package cn.usts.edu.fly.SystemAndRuntime;
import java.util.Properties;
import java.util.Set;
public class SystemDemo {
public static void main(String[] args) {
Properties properties = System.getProperties();
System.out.println(properties);
Set<String> keys = properties.stringPropertyNames();
for (String key : keys) {
String value = System.getProperty(key);
System.out.println(key+"--->"+value);
}
}
}
System.currentTimeMillis()
- System.gc();//内存回收
- System.exit(0);// 程序结束
- System.arraycopy(原数组,目标数组,要复制的起始位置,目标起始位置,复制长度);
package cn.usts.edu.fly.SystemAndRuntime;
import java.util.Properties;
import java.util.Set;
public class SystemDemo {
public static void main(String[] args) {
System.out.println("------------------------------System.currentTimeMillis()-----------------------------------");
long startTime = System.currentTimeMillis();
int sum=0;
for (int i = 0; i < 10000000; i++) {
sum+=i;
}
long endTime = System.currentTimeMillis();
System.out.println("程序运行时间:"+(endTime-startTime)+"毫秒");
}
}
Runtime类
-
用来表示虚拟机的运行状态,用于封装java虚拟机进程,
-
每次使用java命令启动java虚拟机都会产生对应的一个Runtime实例,并且只有一个实例
-
应用程序会通过该实例与运行时的环境相连,应用程序不能创建自己的runtime实例,需要手动创建安
-
Runtime run = Runtime.getRuntime();
package cn.usts.edu.fly.SystemAndRuntime;
import java.io.IOException;
public class RuntimeDemo {
public static void main(String[] args) throws IOException, InterruptedException {
Runtime runtime = Runtime.getRuntime();
System.out.println("处理器个数" + runtime.availableProcessors()+"核");
System.out.println("空闲内存大小" + runtime.freeMemory()+"byte");
System.out.println("最大内存大小" + runtime.maxMemory()+"byte");
Process process = runtime.exec("notepad.exe");
Thread.sleep(3000);
process.destroy();
}
}