nbsp; int a; a = Varargs.add(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); System.out.println(a); } 4 自动实现装箱和解箱操作(Boxing/Unboxing Conversions) 说明:实现了基本类型与外覆类之间的隐式转换。基本类型至外覆类的转换称为装箱,外覆类至基本类型的转换为解箱。这些类包括
Primitive Type Reference Type boolean Boolean byte Byte char Character short Short int Integer long Long float Float double Double
例如,旧的实现方式
Integer intObject;
int intPrimitive; ArrayList arrayList = new ArrayList(); intPrimitive = 11; intObject = new Integer(intPrimitive); arrayList.put(intObject); // 不能放入int类型,只能使Integer 新的实现方式
int intPrimitive;
ArrayList arrayList = new ArrayList(); intPrimitive = 11; //在这里intPrimitive被自动的转换为Integer类型 arrayList.put(intPrimitive); 5 静态导入(Static Imports) 很简单的东西,看一个例子:
没有静态导入
Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));
有了静态导入
import static java.lang.Math.*;
sqrt(pow(x, 2) + pow(y, 2)); 其中import static java.lang.Math.*;就是静态导入的语法,它的意思是导入Math类中的所有static方法和属性。这样我们在使用这些方法和属性时就不必写类名。
需要注意的是默认包无法用静态导入,另外如果导入的类中有重复的方法和属性则需要写出类名,否则编译时无法通过。
6 枚举类(Enumeration Classes) 用法:public enum Name {types, ….}
简单的例子:
public enum Colors {Red, Yellow, Blue, Orange, Green, Purple, Brown, Black}
public static void main(String[] args){ Colors myColor = Colors.Red; System.out.println(myColor); } 又一个简单例子:
import java.util.*;
enum OperatingSystems {windows, unix, linux, macintosh} public class EnumExample1 { public static void main(String args[]) { OperatingSystems os; os = OperatingSystems.windows; switch(os) { case windows: System.out.println(“You chose Windows!”); break; case unix: System.out.println(“You chose Unix!”); break; case linux: System.out.println(“You chose Linux!”); break; case macintosh: System.out.println(“You chose Macintosh!”); break; default: System.out.println(“I don’t know your OS.”); break; } } } 应运enum简写的例子:
import java.util.*;
public class EnumTest { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.print("Enter a size: (SMALL, MEDIUM, LARGE, EXTRA_LARGE) "); String input = in.next().toUpperCase(); Size size = Enum.valueOf(Size.class, input); System.out.println("size=" + size); System.out.println("abbreviation=" + size.getAbbreviation()); if (size == Size.EXTRA_LARGE) System.out.println("Good job--you paid attention to the _."); } }
enum Size { SMALL("S"), MEDIUM("M"), LARGE("L"), EXTRA_LARGE("XL");
private Size(String abbreviation) { this.abbreviation = abbreviation; } public String getAbbreviation() { return abbreviation; } private String abbreviation; } enum类中拥有方法的一个例子:
enum ProgramFlags {
showErrors(0x01), includeFileOutput(0x02), useAlternateProcessor(0x04); private int bit; ProgramFlags(int bitNumber) { bit = bitNumber; } public int getBitNumber() { return(bit); } } public class EnumBitmapExample { public static void main(String args[]) { ProgramFlags flag = ProgramFlags.showErrors; System.out.println(“Flag selected is: “ + flag.ordinal() + “ which is “ + flag.name()); } }
7 元数据(Meta data) 请参考
http://www-900.ibm.com/developerWorks/cn/java/j-annotate1/
http://www-900.ibm.com/developerworks/cn/java/j-annotate2.shtml
8 Building Strings(StringBuilder类) 在JDK5.0中引入了StringBuilder类,该类的方法不是同步(synchronized)的,这使得它比StringBuffer更加轻量级和有效。
9 控制台输入(Console Input) 在JDK5.0之前我们只能通过JOptionPane.showInputDialog进行输入,但在5.0中我们可以通过类Scanner在控制台进行输入操作
例如在1.4中的输入
String input = JOptionPane.showInputDialog(prompt);
int n = Integer.parseInt(input); double x = Double.parseDouble(input); s = input; 在5.0中我们可以
Scanner in = new Scanner(System.in);
System.out.print(prompt); int n = in.nextInt(); double x = in.nextDouble(); String s = in.nextLine(); 10 Covariant Return Types(不晓得怎么翻译,大概是 改变返回类型) JDK5之前我们覆盖一个方法时我们无法改变被方法的返回类型,但在JDK5中我们可以改变它
例如1.4中我们只能
public Object clone() { ... }
... Employee cloned = (Employee) e.clone(); 但是在5.0中我们可以改变返回类型为Employee
public Employee clone() { ... }
... Employee cloned = e.clone(); 11 格式化I/O(Formatted I/O) 增加了类似C的格式化输入输出,简单的例子:
public class TestFormat{
public static void main(String[] args){ int a = 150000, b = 10; float c = 5.0101f, d = 3.14f; System.out.printf("%4d %4d%n", a, b); System.out.printf("%x %x%n", a, b); System.out.printf("%3.2f %1.1f%n", c, d); System.out.printf("%1.3e %1.3e%n", c, d*100); } } 输出结果为:
150000 10
249f0 a
5.01 3.1
5.010e+00 3.140e+02
下面是一些格式化参数说明(摘自Core Java 2 Volume I - Fundamentals, Seventh Edition)
Table 3-5. Conversions for printf
Conversion Character Type Example d Decimal integer 159 x Hexadecimal integer 9f o Octal integer 237 f Fixed-point floating-point 15.9 e Exponential floating-point 1.59E+01 g General floating-point (the shorter of e and f) a Hexadecimal floating point 0x1.fccdp3 s String Hello c Character H b Boolean TRUE h Hash code 42628b2 tx Date and time See Table 3-7 % The percent symbol % n The platform-dependent line separator
Table 3-7. Date and Time Conversion Characters
Conversion Character Type Example C Complete date and time Mon Feb 09 18:05:19 PST 2004 F ISO 8601 date 2004-02-09 D U.S. formatted date (month/day/year) 02/09/2004 T 24-hour time 18:05:19 r 12-hour time 06:05:19 pm R 24-hour tim 上一页 [1] [2] [3] 下一页 没有相关教程
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