System类
System.currentTimeMillis();
System.exit(0);
System.gc();
String javaVersion = System.getProperty("java.version");
System.out.println("java的version:" + javaVersion);
String javaHome = System.getProperty("java.home");
System.out.println("java的home:" + javaHome);
String osName = System.getProperty("os.name");
System.out.println("os的name : " + osName);
String osversion = System.getProperty("os.version");
System.out.println("os的version:" + osversion);
String userName = System.getProperty ("user.name");
System.out.println("user的name:" + userName) ;
String userHome = System.getProperty("user.home");
System.out.println("user的home:" +userHome) ;
BigInteger和BigDecimal
BigDecimal a = new BigDecimal("564655312");
BigDecimal b = new BigDecimal("46456465.486645");
System.out.println(a.divide(b,15,BigDecimal.ROUND_HALF_UP));