1 package test; 2 3 4 /*System类 5 * 6 * public static void gc() 运行垃圾回收器 只有在执行大量的对象的释放,才调用垃圾回收。 7 * public static void exit(int status) 8 * public static void 9 * 10 * */11 12 public class Test01 {13 public static void main(String[] args) {14 Person p=new Person(22,"hello");15 System.out.println(p);16 p=null;17 System.gc();18 19 }20 }
1 package test; 2 3 public class Person { 4 private int age; 5 private String name; 6 public Person() { 7 super(); 8 // TODO Auto-generated constructor stub 9 }10 public Person(int age, String name) {11 super();12 this.age = age;13 this.name = name;14 }15 public int getAge() {16 return age;17 }18 public void setAge(int age) {19 this.age = age;20 }21 public String getName() {22 return name;23 }24 public void setName(String name) {25 this.name = name;26 }27 @Override28 public String toString() {29 return "Person [age=" + age + ", name=" + name + "]";30 }31 public void finalize() throws Throwable{32 System.out.println("当前的对象被回后了"+this);33 super.finalize();34 }35 }
1 package test; 2 3 /*System类 4 * 5 * public static void gc() 运行垃圾回收器 只有在执行大量的对象的释放,才调用垃圾回收。 6 * public static void exit(int status) 终止当前正在运行的jvm, 参数用作状态码,非0表示异常终止 7 * public static long currentTimeMillis() 以毫秒返回当前时间 8 * 9 * 10 * */11 12 public class Test01 {13 public static void main(String[] args) {14 /*System.out.println("hello world");15 System.exit(0);16 System.out.println("accross the great wall");*/17 18 //System.out.println(System.currentTimeMillis()); //144038652502719 20 //得到程序的运行时间21 long start=System.currentTimeMillis();22 for(int i=0;i<1000000;i++){23 System.out.println(i);24 }25 long end=System.currentTimeMillis();26 System.out.println(end-start);27 28 }29 }
1 package test; 2 3 import java.util.Arrays; 4 5 /*System类 6 * 7 8 * 9 * public static void arraycopy(Object src, //数组复制 从指定源数组中复制一个数组,复制从指定的位置开始,到目标数组的指定位置结束。10 int srcPos,11 Object dest,12 int destPos,13 int length)14 * */15 16 public class Test01 {17 public static void main(String[] args) {18 int[] arr={11,22,33,44,55,66,77};19 int[] arr2={2,3,4,5,6,7,8};20 System.arraycopy(arr, 1, arr2, 2, 3);21 System.out.println(Arrays.toString(arr));22 System.out.println(Arrays.toString(arr2));23 }24 }