面試時候雖沒有被問到,但是感覺在相關問題上丟了面試分,在此總結一下。
參考 Reference
http://pwosboy.iteye.com/blog/118756
http://hanhg.iteye.com/blog/291956
http://pengcqu.iteye.com/blog/499749
Java 1.5
1. Generic
在之前版本,如果聲明的時候沒有特別指出class,比如ArrayList list = new ArrayList(),那麼取出數據的時候需要對其進行類型轉換。
list.add(new Integer(3));
Integer temp = (Integer)list.get(0);
現在
ArrayList<Integer> list = new ArrayList<Integer>();
注意一下下列這種情況
public <T extends Comparable> T max(T t1, T t2) {
if (t1.compareTo(t2) > 0)
return t1;
else
return t2;
}
void printCollection(Collection<?> c) {// Collection<?>, collection of unknown
for (Object e : c) {
System.out.println(e);
}
}// 可以傳入各種類型的Collection,如果是Collection<Object>則不能這麼用,因爲“若Foo是Bar的一個子類型(子類或子接口), G是某個泛型聲明, 則G<Foo>並不是G<Bar>的一個子類型”
2. For each
ArrayList<Integer> list = new ArrayList<Integer>();
list.add(new Integer(3));
list.add(new Integer(4));
for(Integer temp : list){
System.out.println(temp.intValue());
}
3. Autoboxing/unboxing
自動裝包:基本類型自動轉爲包裝類.(int >> Integer)
自動拆包:包裝類自動轉爲基本類型.(Integer >> int)
int a = 3;
Collection<Integer> c = new ArrayList<Integer>();
c.add(a);//自動轉換成Integer.
Integer b = new Integer(2);
c.add(b + 2);//這裏Integer先自動轉換爲int進行加法運算,然後int再次轉換爲Integer.
4. enum
public enum Color{
Red,
White,
Blue
}
for (Color c : Color.values())
System.out.println(c);
5. Varargs
public void write(Object... objs) {
for (Object obj: objs)
System.out.println(obj);
}
6. Static Imports
import static java.lang.Math.*;
…….
r = sin(PI * 2); //無需再寫r = Math.sin(Math.PI);
Java 1.6
1. Class Desktop && Class SystemTray
2. JAXB2
3. StAX (DOM, SAX)
4. Compiler API
5. Http Server API
6. Pluggable Annotation Processing API
7. java.io.Console
8. Support script language: Ruby, Groovy, Javascript
9. Common Annotations
1.7
1.集合的支持
List< String> list = ["item"];
String item = list[0];
Set< String > set = {"item"};
Map< String,Integer > map = {"key" : 1};
int value = map["key"];
2. 資源自動回收管理
之前:
BufferedReader br = new BufferedReader(new FileReader(path));
try {
return br.readLine();
} finally {
br.close();
}
Java 1.7:
try (BufferedReader br = new BufferedReader(new FileReader(path))) {
return br.readLine();
}
3. Generic simplified
Map<String,String> hello = new Map<>();
4. 數字中的下劃線
待研究
5. switch case支持String. Remember to check if null before parse String
6. Binary symbol
int binary = 0b1001_1001;
7. Catch mutiple exception types
try {
do something;
}
catch(IOException | NullPointerException | ..........) {
do something;
}