jdk1.7和jdk1.8区别
在jdk7的新特性方面主要有一下几方面的增强
本文是我学习了解了jdk7和jdk8的一些新特性的一些资料，有兴趣的大家可以浏览下下面的内容。官方文档
- 在jdk7的新特性方面主要有下面几方面的增强：
-
jdk1.7语法上
1.1 二进制变量的表示，支持将整数类型用二进制来表示，以0b开头。
所有整数int、short、long、byte都可以用二进制表示
// An 8-bit 'byte' value: byte aByte = (byte) 0b00100001;```// A 16-bit 'short' value:
short aShort = (short) 0b1010000101000101;// Some 32-bit 'int' values:
intanInt1 = 0b10100001010001011010000101000101;
intanInt2 = 0b101;
intanInt3 = 0B101; // The B can be upper or lower case.// A 64-bit 'long' value. Note the "L" suffix:
long aLong = 0b1010000101000101101000010100010110100001010001011010000101000101L;// 二进制在数组等的使用
final int[] phases = { 0b00110001, 0b01100010, 0b11000100, 0b10001001,
0b00010011, 0b00100110, 0b01001100, 0b10011000 };1.2 Switch语句支持String类型public void 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;
}1.3 Try-with-resource语句 > 注意：实现java.long.AutoCloseable接口的资源都可以放到try中， 跟final里面的关闭资源类似；按照声明逆序关闭资源；Try块抛出的异常Throwable.getSuppressed获取。
try (java.util.zip.ZipFile zf = new java.util.zip.ZipFile(zipFileName);
java.io.BufferedWriter writer = java.nio.file.Files
.newBufferedWriter(outputFilePath, charset)) {
// Enumerate each entry
for (java.util.Enumeration entries = zf.entries(); entries
.hasMoreElements();) {
// Get the entry name and write it to the output file
String newLine = System.getProperty("line.separator");
String zipEntryName = ((java.util.zip.ZipEntry) entries
.nextElement()).getName() + newLine;
writer.write(zipEntryName, 0, zipEntryName.length());
}
}
```
1.4 Catch多个异常 说明：Catch异常类型为final； 生成Bytecode 会比多个catch小； Rethrow时保持异常类型
```
public static void main(String[] args) throws Exception {
try {
testthrows();
} catch (IOException | SQLException ex) {
throw ex;
}
}
public static void testthrows() throws IOException, SQLException {
}
```
1.5 数字类型的下划线表示 更友好的表示方式，不过要注意下划线添加的一些标准，可以参考下面的示例
```
long creditCardNumber = 1234_5678_9012_3456L;
long socialSecurityNumber = 999_99_9999L;
float pi = 3.14_15F;
long hexBytes = 0xFF_EC_DE_5E;
long hexWords = 0xCAFE_BABE;
long maxLong = 0x7fff_ffff_ffff_ffffL;
byte nybbles = 0b0010_0101;
long bytes = 0b11010010_01101001_10010100_10010010;
//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
```
1.6 泛型实例的创建可以通过类型推断来简化 可以去掉后面new部分的泛型类型，只用<>就可以了。
```
List strList = new ArrayList();
List<String> strList4 = new ArrayList<String>();
List<Map<String, List<String>>> strList5 = new ArrayList<Map<String, List<String>>>();
```
```
//编译器使用尖括号 (<>) 推断类型
List<String> strList0 = new ArrayList<String>();
List<Map<String, List<String>>> strList1 = new ArrayList<Map<String, List<String>>>();
List<String> strList2 = new ArrayList<>();
List<Map<String, List<String>>> strList3 = new ArrayList<>();
List<String> list = new ArrayList<>();
list.add("A");
// The following statement should fail since addAll expects
// Collection<? extends String>
//list.addAll(new ArrayList<>());
```
1.7 在可变参数方法中传递非具体化参数,改进编译警告和错误
Heap pollution 指一个变量被指向另外一个不是相同类型的变量。例如
```
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
Jdk7:
public static <T> void addToList (List<T> listArg, T... elements) {
for (T x : elements) {
listArg.add(x);
}
}
```
> 你会得到一个warning
warning: [varargs] Possible heap pollution from parameterized vararg type
要消除警告，可以有三种方式
1.加 annotation @SafeVarargs
2.加 annotation @SuppressWarnings({"unchecked", "varargs"})
3.使用编译器参数 –Xlint:varargs;
1.8 信息更丰富的回溯追踪 就是上面try中try语句和里面的语句同时抛出异常时，异常栈的信息
```
java.io.IOException
* at Suppress.write(Suppress.java:19)
* at Suppress.main(Suppress.java:8)
* Suppressed: java.io.IOException
* at Suppress.close(Suppress.java:24)
* at Suppress.main(Suppress.java:9)
* Suppressed: java.io.IOException
* at Suppress.close(Suppress.java:24)
* at Suppress.main(Suppress.java:9)
```
2. ThreadLocalRandon 并发下随机数生成类，保证并发下的随机数生成的线程安全，实际上就是使用threadlocal
final int MAX = 100000;
ThreadLocalRandom threadLocalRandom = ThreadLocalRandom.current();
long start = System.nanoTime();
for (int i = 0; i < MAX; i++) {
threadLocalRandom.nextDouble();
}
long end = System.nanoTime() - start;
System.out.println("use time1 : " + end);
long start2 = System.nanoTime();
for (int i = 0; i < MAX; i++) {
Math.random();
}
long end2 = System.nanoTime() - start2;
System.out.println("use time2 : " + end2);
