JDK7新特性

jdk新特性(1.4-1.8)

1,Binary Literals 二进制类型的支持

1-1 支持四种数据类型： byte, short, int, and long

前缀用 0b or 0B

// An 8-bit 'byte' value:
byte aByte = (byte)0b00100001;

// A 16-bit 'short' value:
short aShort = (short)0b1010000101000101;

// Some 32-bit 'int' values:
int anInt1 = 0b10100001010001011010000101000101;
int anInt2 = 0b101;
int anInt3 = 0B101; // The B can be upper or lower case.

// A 64-bit 'long' value. Note the "L" suffix:
long aLong = 0b1010000101000101101000010100010110100001010001011010000101000101L;

该四种数据类型的数组同样也是支持二进制类型的

public static final int[] phases = {
0b00110001,
0b01100010,
0b11000100,
0b10001001,
0b00010011,
0b00100110,
0b01001100,
0b10011000
}

1-2 You can use binary literals to make a bitmap more readable

使用二进制类型表示图片，使bitmap更具可读性

public static final short[] HAPPY_FACE = {
(short)0b0000011111100000;
(short)0b0000100000010000;
(short)0b0001000000001000;
(short)0b0010000000000100;
(short)0b0100000000000010;
(short)0b1000011001100001;
(short)0b1000011001100001;
(short)0b1000000000000001;
(short)0b1000000000000001;
(short)0b1001000000001001;
(short)0b1000100000010001;
(short)0b0100011111100010;
(short)0b0010000000000100;
(short)0b0001000000001000;
(short)0b0000100000010000;
(short)0b0000011111100000;
}

2，整数类型可以用_进行分割，方便阅读。

_ 仅仅用在两个数字之间。

不能用的地方：

At the beginning or end of a number
Adjacent to a decimal point in a floating point literal
Prior to an F or L suffix
In positions where a string of digits is expected

1，数字的开始或者结尾。
2，小数点两侧
3，字符F或者L前后
4，数字字符串不被使用   String age = "23"

float pi1 = 3_.1415F;      // Invalid; cannot put underscores adjacent to a decimal point
float pi2 = 3._1415F;      // Invalid; cannot put underscores adjacent to a decimal point
long socialSecurityNumber1
= 999_99_9999_L;         // Invalid; cannot put underscores prior to an L suffix

int x1 = _52;              // This is an identifier, not a numeric literal
int x2 = 5_2;              // OK (decimal literal)
int x3 = 52_;              // Invalid; cannot put underscores at the end of a literal
int x4 = 5_______2;        // OK (decimal literal)

int x5 = 0_x52;            // Invalid; cannot put underscores in the 0x radix prefix
int x6 = 0x_52;            // Invalid; cannot put underscores at the beginning of a number
int x7 = 0x5_2;            // OK (hexadecimal literal)
int x8 = 0x52_;            // Invalid; cannot put underscores at the end of a number

int x9 = 0_52;             // OK (octal literal)
int x10 = 05_2;            // OK (octal literal)
int x11 = 052_;            // Invalid; cannot put underscores at the end of a number

3, switch 语句支持String类型

public String getTypeOfDayWithSwitchStatement(String dayOfWeekArg) {
String typeOfDay;
switch (dayOfWeekArg) {
case "Monday":
typeOfDay = "Start of work week";
break;
case "Tuesday":
case "Wednesday":
case "Thursday":
typeOfDay = "Midweek";
break;
case "Friday":
typeOfDay = "End of work week";
break;
case "Saturday":
case "Sunday":
typeOfDay = "Weekend";
break;
default:
throw new IllegalArgumentException("Invalid day of the week: " + dayOfWeekArg);
}
return typeOfDay;
}

4，Type Inference for Generic Instance Creation 类型推断用于泛型实例创建

比如 java集合类：

Map<String, List<String>> myMap = new HashMap<String, List<String>>();

在jdk7中：
Map<String, List<String>> myMap = new HashMap<>();

List<String> list = new ArrayList<>();
list.add("A");
list.addAll(new ArrayList<>()); // 报错
list.addAll(list);

自定义泛型类

class MyClass<X> {
<T> MyClass(T t) {
// ...
}
}

创建实例：
MyClass<Integer> myObject = new MyClass<>("");
MyClass<String> myObject = new MyClass<>("");

5，Improved Compiler Warnings and Errors When Using Non-Reifiable Formal Parameters with Varargs Methods

编译器会提高警告和错误，在你使用非具体化参数(泛型)同时也是可变参数时。

比如：(T… elements)

该页包含几个专题：

1，堆污染，堆错误

2，可变参数和非具体化参数(泛型参数)

3，泛型可变参数潜在漏洞

4，当使用泛型可变参数提出安全警告

1，堆污染

List l = new ArrayList<Number>();
List<String> ls = l;       // unchecked warning
l.add(0, new Integer(42)); // another unchecked warning
String s = ls.get(0);      // ClassCastException is thrown

错误点：1，l赋值给ls。2，add方法。

2，可变参数和非具体化参数(泛型参数)

public class ArrayBuilder {

public static <T> void addToList (List<T> listArg, T... elements) {
for (T x : elements) {
listArg.add(x);
}
}

public static void faultyMethod(List<String>... l) {
Object[] objectArray = l;  // Valid
objectArray[0] = Arrays.asList(new Integer(42));
String s = l[0].get(0);    // ClassCastException thrown here
}

}

3，泛型可变参数潜在漏洞

public static void faultyMethod(List<String>... l) {
Object[] objectArray = l;  //Valid
objectArray[0] = Arrays.asList(new Integer(42));
String s = l[0].get(0);    // ClassCastException thrown here
}

4,当使用泛型可变参数提出安全警告,添加警告注解

@SafeVarargs

@SuppressWarnings(“unchecked”)

@SuppressWarnings(“varargs”) 这个使用编译参数：-Xlint:varargs

6，The try-with-resources Statement

主要就是资源的自动回收

语法： try(资源) 注意区别try{}catch{}

备注：该资源必须实现了AutoCloseable or Closeable 接口

例子：

在finally中关闭BufferedReader

static String readFirstLineFromFileWithFinallyBlock(String path) throws IOException {
BufferedReader br = new BufferedReader(new FileReader(path));
try {
return br.readLine();
} finally {
if (br != null) br.close();
}
}

try-with-resources 语句：

Classes That Implement the AutoCloseable or Closeable Interface

static String readFirstLineFromFileWithFinallyBlock(String path) throws IOException {
try(BufferedReader br = new BufferedReader(new FileReader(path))) {
return br.readLine();
}
}

7,Catching Multiple Exception Types and Rethrowing Exceptions with Improved Type Checking

合并多异常和改良重抛异常检查

1，合并多异常

catch (IOException ex) {
logger.log(ex);
throw ex;
} catch (SQLException ex) {
logger.log(ex);
throw ex;
}

在JDK7中：
catch (IOException|SQLException ex) {
logger.log(ex);
throw ex;
}

2，重抛异常

static class FirstException extends Exception { }
static class SecondException extends Exception { }

public void rethrowException(String exceptionName) throws Exception {
try {
if (exceptionName.equals("First")) {
throw new FirstException();
} else {
throw new SecondException();
}
} catch (Exception e) {
throw e;
}
}

在JDK7中：
public void rethrowException(String exceptionName)
throws FirstException, SecondException {
try {
// ...
}
catch (Exception e) {
throw e;
}
}