1 ,菱形語法(泛型實例化類型自動推斷)
- List<String> list = new ArrayList<>(); // <>這個真的很像菱形
List<String> list = new ArrayList<>(); // <>這個真的很像菱形
2 ,在目前版本中,不可具體化的泛型(任意類型)可變參數,在編譯時,會在調用處產生警告, JDK7 裏將這個警告挪到了方法定義處。
變化前:
- static <T> List<T> asList(T... elements) { ... }
- static List<Callable<String>> stringFactories() {
- Callable<String> a, b, c;
- ...
- // 警告處
- return asList(a, b, c);
- }
static <T> List<T> asList(T... elements) { ... }
static List<Callable<String>> stringFactories() {
Callable<String> a, b, c;
...
// 警告處
return asList(a, b, c);
}
變化後:
- // 警告處
- static <T> List<T> asList(T... elements) { ... }
- static List<Callable<String>> stringFactories() {
- Callable<String> a, b, c;
- ...
- return asList(a, b, c);
- }
// 警告處
static <T> List<T> asList(T... elements) { ... }
static List<Callable<String>> stringFactories() {
Callable<String> a, b, c;
...
return asList(a, b, c);
}
3 ,字符串終於可以 switch 啦 .
- String s = ...
- switch (s) {
- case "quux" :
- processQuux(s); //沒有break,繼續往下
- case "foo" :
- case "bar" :
- processFooOrBar(s);
- break ;
- case "baz" :
- processBaz(s); //沒有break,繼續往下
- default :
- processDefault(s);
- break ;
- }
String s = ...
switch(s) {
case "quux":
processQuux(s); //沒有break,繼續往下
case "foo":
case "bar":
processFooOrBar(s);
break;
case "baz":
processBaz(s); //沒有break,繼續往下
default:
processDefault(s);
break;
}
4 ,支持二進制語法和單位級別的數字表示方式
- // 8位byte
- byte aByte = ( byte )0b00100001;
- // 16位short
- short aShort = ( short )0b1010000101000101;
- // 32位int
- int anInt1 = 0b10100001010001011010000101000101;
// 8位byte
byte aByte = (byte)0b00100001;
// 16位short
short aShort = (short)0b1010000101000101;
// 32位int
int anInt1 = 0b10100001010001011010000101000101;
支持單位級別的數字,提高可讀性
- long underScores = 9_223_372_036_854_775_807L; // 每三位加一下劃線,等同於 9,223,372,036,854,775,807
long underScores = 9_223_372_036_854_775_807L; // 每三位加一下劃線,等同於 9,223,372,036,854,775,807
5 ,從語法層面上支持集合,不再是數組的專利。
- final List<Integer> piDigits = [ 3 , 1 , 4 , 1 , 5 , 9 , 2 , 6 , 5 , 3 , 5 , 9 ];
- final Set<Integer> primes = { 2 , 7 , 31 , 127 , 8191 , 131071 , 524287 };
- final Map<Integer, String> platonicSolids = { 4 : "tetrahedron" ,
- 6 : "cube" , 8 : "octahedron" , 12 : "dodecahedron" , 20 : "icosahedron"
- };
final List<Integer> piDigits = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 9];
final Set<Integer> primes = { 2, 7, 31, 127, 8191, 131071, 524287 };
final Map<Integer, String> platonicSolids = { 4 : "tetrahedron",
6 : "cube", 8 : "octahedron", 12 : "dodecahedron", 20 : "icosahedron"
};
6 , JSR 292 動態類型語言支持
- Dynamic x = (動態語言腳本);
- Object y = x.foo("ABC" ).bar( 42 ).baz();
Dynamic x = (動態語言腳本);
Object y = x.foo("ABC").bar(42).baz();
7 ,動態資源管理
在目前版本的 java 中,當你操作流時,一定會加 try..finally 以保證出現異常時,流能被正確關閉。
- BufferedReader br = new BufferedReader( new FileReader(path));
- try {
- return br.readLine();
- } finally {
- br.close();
- }
BufferedReader br = new BufferedReader(new FileReader(path));
try {
return br.readLine();
} finally {
br.close();
}
在 JDK7 裏,你只需要將資源定義在 try() 裏, Java7 就會在 readLine 拋異常時,自動關閉資源。
另外,資源類必須實現 Disposable<?> 接口。支持管理多個資源。
- try (BufferedReader br = new BufferedReader( new FileReader(path)) {
- return br.readLine();
- }
try (BufferedReader br = new BufferedReader(new FileReader(path)) {
return br.readLine();
}