Class System 方法学习

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Static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)

复制一个数组的部分到指定数组的指定位置

public class FirstJava {       public static void main(String[] args) {              int[] fun = {0,1,2,3,4,5,6};              System.arraycopy(fun,0,fun,3,2);              for (int i=0; i < fun.length; i++) {                     System.out.println(fun[i]);              }       }}

static String clearProperty(String key)

方法将删除由指定的键指定的系统属性

public class FirstJava {       public static void main(String[] args) {              System.setProperty("akke","abc");              System.out.println("using getProperty: "+ System.getProperty("akke"));              System.clearProperty("akke");              System.out.println("using getProperty: "+ System.getProperty("akke"));       }}

static Console console()

Returns the unique Console object associated with the current Java virtual machine, if any.

java.io.Console 只能用在标准输入、输出流未被重定向的原始控制台中使用，在 Eclipse 或者其他 IDE 的控制台是用不了的。

import java.io.Console;import java.io.PrintWriter;  public class NewJava {      public static void main(String[] args) {          Console cons = System.console();          if (cons != null) {              // -------------------------              PrintWriter printWriter = cons.writer();              printWriter.write("input:");              cons.flush();              // -------------------------              String str1 = cons.readLine();              // -------------------------              cons.format("%s", str1);          }      }  }

static long currentTimeMillis()

以毫秒返回现在的时间(自1970年1月1日0时起的毫秒数)

public class FirstJava {       public static void main(String[] args) {              System.out.println("currentTime: "+ System.currentTimeMillis());       }}

static void exit(int status)

结束正在运行的虚拟机

static void gc()

运行垃圾回收器
//告诉垃圾收集器打算进行垃圾收集，而垃圾收集器进不进行收集是不确定的

static Map

import java.util.Map;public class FirstJava {       public static void main(String[] args) {              Map<String, String> env = System.getenv();              for(String key : env.keySet()){   //只能遍历key                     System.out.println("Key = "+key);              }              for(Object value : env.values()){  //只能遍历value                     System.out.println("Value = "+value);              }       }}

输出一个Map:http://blog.csdn.net/b_h_l/article/details/7593970

static String getenv(String name)

获得指定环境变量名的值

static Properties getproperties()

确认现在的系统变量

public class FirstJava {       public static void main(String[] args) {              Properties pps = System.getProperties();              pps.list(System.out);       }}

static String getProperty(String key)

通过指定键获得系统变量

static String getProperty(String Key, String def)

通过指定键获得系统变量，如果相应的值不存在，则用def(ault)初始化该变量

static SecurityManager getSecurityManager()

获得当前系统的安全管理者，如果该管理者不存在，则返回null

public class FirstJava {       public static void main(String[] args) {              SecurityManager securityManager = System.getSecurityManager();              if(securityManager!=null)                     System.out.print(securityManager.toString());              else                     System.out.println("empty");       }}

###static int identityHashCode(Object x)

根据对象返回hashCode()

public class TestSystemHashCode {    public static void main(String[] args) {        String a = new String("hhh");        String b = new String("hhh");        System.out.println(System.identityHashCode(a));        System.out.println(System.identityHashCode(b));        System.out.println(a.hashCode());        System.out.println(b.hashCode());        //输出不同        String string1 = "wxg";        String string2 = "wxg";        System.out.println(System.identityHashCode(string1));        System.out.println(System.identityHashCode(string2));        System.out.println(string1.hashCode());        System.out.println(string2.hashCode());        //输出相同        }    }

static Channel inheritedChannel()

???

public class FirstJava {       public static void main(String[] args) throws IOException {              Channel channel = System.inheritedChannel();              if(channel!=null)                     System.out.print("not empty");              else                     System.out.println("empty");       }}

static String lineSeparator()

返回系统资源（换行符）

public class FirstJava {       public static void main(String[] args) throws IOException {              String lineseparator = System.lineSeparator();              if(lineseparator!=null)                     System.out.print("first line"+lineseparator+"second line");              else                     System.out.println("empty");       }}

static void load(String filename)

static void loadLibrary(String libname)

调用其他运行库

static String mapLobraryName(String libname)

返回一个与平台相关的本地库的名字

public class FirstJava {       public static void main(String[] args) {              // prints the name of the Operating System              System.out.println(System.getProperty("os.name"));     /* maps a library name into a platform-specific string representing     a native library */              String str = System.mapLibraryName("os.name");              System.out.println(str);       }}

static long nanoTime()

返回最准确的可用系统计时器的当前值，以毫微秒为单位。
这个返回值是一个从确定的值算起的，但是这个值是任意的，可能是一个未来的时间，所以返回值有可能是负数。

public class FirstJava {       public static void main(String[] args) {              long l = System.nanoTime();              System.out.print(l);       }}

static void runFinalization()

//强制调用已经失去引用的对象的finalize方法
///（选择性的）被调用在gc之前

static void setErr(PrintStream err)

重新分配“标准”错误输出流

static void setIn(InputStraem in)

重新分配“标准”输入流

static void setOut(printStream out)

重新分配“标准”输出流

import java.lang.*;import java.io.*;public class SystemDemo {   public static void main(String[] args) throws Exception {     // create file     FileOutputStream f = new FileOutputStream("file.txt");     System.setOut(new PrintStream(f));     // this text will get redirected to file     System.out.println("This is System class!!!");     // existing file     System.setIn(new FileInputStream("file.txt"));     // read the first character in the file     char ret = (char)System.in.read();     // returns the first character     System.out.println(ret);         // create a file     FileOutputStream f = new FileOutputStream("file.txt");     System.setErr(new PrintStream(f));     // redirect the output     System.err.println("This will get redirected to file");   }   }}

static void setProperties(properties props)

static String setProperty(String key, String value)

设置系统属性的属性参数

public class SystemDemo {   public static void main(String[] args) {     // prints Java Runtime Version before property set     System.out.print("Previous : ");     System.out.println(System.getProperty("java.runtime.version"));     Properties p = System.getProperties();     p.put("java.runtime.version", "Java Runtime 1.6.0");     System.setProperties(p);     // prints Java Runtime Version after property set     System.out.print("New : ");     System.out.println(System.getProperty("java.runtime.version"));   }} public class SystemDemo {   public static void main(String[] args) {     // prints Java Runtime Version before property set     System.out.print("Previous : ");     System.out.println(System.getProperty("java.runtime.version" ));     System.setProperty("java.runtime.version", "Java Runtime 1.6.0");     // prints Java Runtime Version after property set     System.out.print("New : ");     System.out.println(System.getProperty("java.runtime.version" ));   }}

static void setSecurityManager(SecurityManager s)

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