Java 新功能

Posted by Bruce Tsai

Java 5

• 自動裝箱／拆箱 (Auto-Boxing/Unboxing)

int number = new Integer(10);
Integer value = 10;

• 泛型 (Generic Types)

List<String> list = new ArrayList<String>();

• 註釋 (Annotation)

@Description
public String getTypeName(){
   ...
}

• 列舉類型 (enum)

public enum Gender {
    Male, Female
}

• 輸入輸出 (Scanner / Formatter)

String str = String.format("Hi %s", name);

• foreach 迴圈

// 4 以前
for (int i = 0; i < list.size(); i++) {
    // do something
}
// 5
for (Object value : list) {
    // do somthing
}

• 可變長度的引數

String call(String name, int... values) {
    // do something
}

• static 引入

import static java.lang.Math.*;

double r = cos(PI * theta);

Java 6

• Instrumentation
• HTTP 增強
• JMX 與系統管理
• 編譯器 API
• Java DB 和 JDBC 4.0
• 對腳本語言的支持
• XML API 與 Web 服務

Java 7

• Diamond Operator

// 6 以前
List<String> list = new ArrayList<String>();
// 7 
List<String> list = new ArrayList<>();

• switch 字串支援

String value = getValue();
switch (value) {
    case "10":
        // do something
        break;
    case "20":
        // do something
        break;
}

• Multi-catch

// 6 以前
try {
    execute();
} catch (FileNotFoundException e) {
    e.printStackTrace();
} catch (InterruptedIOException e) {
    e.printStackTrace();
}
// 7
try {
    execute();
} catch (FileNotFoundException | InterruptedIOException e) {
    e.printStackTrace();
}

• try-with-resource 語法／java.lang.AutoCloseable／自動資源管理(ARM)

// 定義
public class Lock implements AutoCloseable {
    public void close() throws Exception {
        // close lock
    }
}
// 使用
try (Lock lock = new Lock()) {
    // do something
} catch (Exception e) {
    e.printStackTrace();
}
try (FileInputStream fis = new FileInputStream(file);
     BufferedInputStream bis = new BufferedInputStream(fis)) {
    // do something
} catch (Exception e) {
    e.printStackTrace();
}

• 支援二進制數值／數值分割（Enhanced syntax for numeric literals）

int value = 0b1010100;
long anotherLong = 2_147_483_648L;

• New file system API (NIO 2.0)

Path path= Paths.get("c:\Temp\temp");

Java 8

• Lambda Expressions

Runnable r = () -> {
    // do something
};

相似功能參考 Retrolambda

• Method Reference

List<String> names = getNames();
names.forEach(System.out::println);

• Streams

List<String> strings =
    Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
List<String> filtered = strings.stream()
                .filter(string -> !string.isEmpty())
                .collect(Collectors.toList());

相似功能參考 Guava 及 Apach Commons Functor

• New Date / Time APIs

LocalDateTime currentTime = LocalDateTime.now();

相似功能參考 Joda-Time

• Default Methods

public interface vehicle {
   default void print(){
      System.out.println("I am a vehicle!");
   }
}