3 可变参数(Variable Arguments)
实现了更灵活的方法参数传入方式,System.out.printf是个很好的例子 用法:void test(Object … args) 一个很容易理解的例子public static int add(int ... args){ int total = 0;
for (int i = 0; i < args.length; i++)
total += args[i];
return total;
}
public static void main(String[] args){
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;
file://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.shtml8 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Employeepublic 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 10249f0 a5.01 3.15.010e+00 3.140e+02
实现了更灵活的方法参数传入方式,System.out.printf是个很好的例子 用法:void test(Object … args) 一个很容易理解的例子public static int add(int ... args){ int total = 0;
for (int i = 0; i < args.length; i++)
total += args[i];
return total;
}
public static void main(String[] args){
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;
file://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.shtml8 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Employeepublic 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 10249f0 a5.01 3.15.010e+00 3.140e+02
解决方案 »
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