Java常用类(7)- System类
System类
System系统类,主要用于获取系统的熟悉数据和其他操作,构造方法私有
复制数组
System.arraycopy()
package commonclass.systemclass; import java.util.Arrays; public class Demo01 { public static void main(String[] args) { //arraycopy:数组的复制 /* src:源数组 srcPos:从哪个位置开始复制 dest:目标数组 destPos:目标数组的位置 length:复制的长度 System.arraycopy(src,srcPos,dest,destPos,length); */ int arr[] = {0,1,2,3,4}; int dest[] = new int[8]; System.arraycopy(arr,0,dest,0,arr.length); System.out.println(Arrays.toString(dest)); for (int i:dest) { System.out.print(i+" "); } } }
获取系统时间毫秒数
System.currentTimeMillis():常用于计算系统运行时间
package commonclass.systemclass; import java.util.concurrent.ForkJoinPool; public class Demo02 { public static void main(String[] args) { long start=System.currentTimeMillis(); for (int i = 0; i < 9999; i++) { for (int j = 0; j <99999 ; j++) { int result = i+j; } } long end = System.currentTimeMillis(); System.out.println("系统用时:"+(end-start)); } }
垃圾回收器
System.gc():告诉垃圾回收器回收
package commonclass.systemclass; public class Student { private String name; private int age; public Student(String name, int age) { this.name = name; this.age = age; } public Student() { } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public String toString() { return "Student{" + "name='" + name + '\'' + ", age=" + age + '}'; } //垃圾回收器 @Override protected void finalize() throws Throwable { System.out.println("回收了"+name+"/t"+age); } }
package commonclass.systemclass; public class Person { public static void main(String[] args) { //垃圾对象,没有用 new Student("aaa",22); new Student("bbb",23); new Student("ccc",32); //通知垃圾回收器回收 System.gc(); } }
退出JVM
exit():0表示正常退出,非0表示异常退出
package commonclass.systemclass; public class Demo03 { public static void main(String[] args) { System.exit(0); //👆已经退出了 ,所以👇代码不执行 System.out.println("geLaoTao"); } }
补充:后面还有流的笔记,会再完善System常用方法