Java7-11新语法特性

Java 7

1. 以前泛型初始化比较麻烦，现在对于Map<String, List<Trade>> trades = new TreeMap<String, List<Trade>> ();这种初始化，可以直接推测Map<String, List<Trade>> trades = new TreeMap <> ();

2. 引入switch

public class StringInSwitchStatementExample {  
    public static void main(String[] args) {  
        String game = "Card-Games";  
        switch(game){  
        case "Hockey": case"Cricket": case"Football":  
            System.out.println("This is a outdoor game");  
            break;  
        case "Chess": case"Card-Games": case"Puzzles": case"Indoor basketball":  
            System.out.println("This is a indoor game");  
            break;  
        default:   
            System.out.println("What game it is?");  
        }  
    }  
}  

　　

3. 自动资源分配 try(someresource)，不需要再用try{...}finally{close()}

还可以用；分割来一次申请多个资源，比如: try(FileOutputStream fos = newFileOutputStream("movies.txt");DataOutputStream dos = newDataOutputStream(fos)) {

不过这些资源需要实现AutoCloseable接口（是java.io.Closeable的父接口）。

4. 引入数字常量中的下划线，比如1_000_000

5. 在一个catch中catch多种exception。catch(ExceptionOne | ExceptionTwo | ExceptionThree e) 

6. 新的File System API（nio2.0)

比如：

Path path= Paths.get("c:Temp	emp");
path.getNameCount();//2
path.getFileName();//temp.txt
path.getRoot();//c:
path.getParent();//c:Temp

Files.delete(path);
Files.deleteIfExists(path)
Files.copy(srcpath, despath)
Files.move(srcpath, despath)
Files.createSymbolicLink(symLink, srcpath)

能用WatchService来获取dir或者file变更的通知

WatchService  watchService = FileSystems.getDefault().newWatchService();
dirToWatch.register(watchService, ENTRY_CREATE, ENTRY_MODIFY, ENTRY_DELETE);

while(true)
{
    WatchKey key = watchService.take();
    for(WatchEvent<?> event : key.pollEvents()) {
        Kind<?> kind = event.kind();
        //do sth
    }
　　key.reset();
} 

7. ForkJoinTask & ForkJoinPool

ForkJoinTask可以是RecursiveAction或者RecursiveTask，这里前者不返回

ForkJoinPool Pool = new ForkJoinPool(proc);  
TaskA tk=new TaskA(arg1);
T t = Pool.invoke(tk); 
Pool.awaitTermination(3, TimeUnit.SECONDS);
Pool.awaitQuiescence(2, TimeUnit.SECONDS);
Pool.getActiveThreadCount();
Pool.getPoolSize();
Pool.isTerminating();
TaskA tk2=new TaskA(arg1);
Pool.execute(tk2); // do not return
Pool.getAsyncMode()//if FIFO
Pool.submit(tk3);
Pool.shutdown();

class TaskA extends RecursiveTask<T> {
    TaskA(T argT) { } 
    protected T compute() {
        return new T();
    }
}

ForkJoinPool fpool = new ForkJoinPool();
TaskA tk = new TaskA();
ForkJoinTask<String> Sfpool = ForkJoinTask.adapt(tk,"OK");
fpool.invoke(Sfpool);    
if(Sfpool.isDone())    
System.out.println(Sfpool.join()); //OK，功效相当于在tk结束之后返回一个OK   

这里ForkJoinTask.adapt提供一个运行Runnable并且返回可选的预定result的新ForkJoinTask。

8. invokeDynamic，此外，Java 7引入了新的java.lang.invoke包，里面有MethodHandle和CallSite等功能。

public class Main { 

    public static void main(String[] args) {
        long lengthyColors = List.of("Red", "Green", "Blue")
          .stream().filter(c -> c.length() > 3).count();
    }
}

　　

javap -c -p Main
// truncated
// class names are simplified for the sake of brevity 
// for instance, Stream is actually java/util/stream/Stream
0: ldc               #7             // String Red
2: ldc               #9             // String Green
4: ldc               #11            // String Blue
6: invokestatic      #13            // InterfaceMethod List.of:(LObject;LObject;)LList;
9: invokeinterface   #19,  1        // InterfaceMethod List.stream:()LStream;
14: invokedynamic    #23,  0        // InvokeDynamic #0:test:()LPredicate;
19: invokeinterface  #27,  2        // InterfaceMethod Stream.filter:(LPredicate;)LStream;
24: invokeinterface  #33,  1        // InterfaceMethod Stream.count:()J
29: lstore_1
30: return

　　

这里filter新建了一个Predicate实例，并且调用了invokedynamic。调用对象是一个匿名成员函数，在BootstrapMethod Table的第0个。

private static boolean lambda$main$0(java.lang.String);
    Code:
       0: aload_0
       1: invokevirtual #37                 // Method java/lang/String.length:()I
       4: iconst_3
       5: if_icmple     12
       8: iconst_1
       9: goto          13
      12: iconst_0
      13: ireturn

引用来自https://www.baeldung.com/java-invoke-dynamic

 当ＪＶＭ第一次看到invokeDynamic的时候会调用一个特殊的方法Bootstrap来进行初始化。Bootstrap是用来invocation process的，可以包含任何逻辑。当bootstrap调用完成之后，会返回一个CallSite实例，这个CallSite实例中封装了以下信息：

1. 指向JVM应当执行的实际逻辑的指针MethodHandle

2. 条件变量，用来指示CallSite是否可用。

之后JVM就不会再次调用bootstrap而是会直接用CallSite中的MethodHandle了。

与Reflection不同，JVM会试着优化MethodHandle中的代码。

此时列出BootstrapTable。可以看到，所有bootstrap method都存在LambdaMetafactory.metafactory里面。

javap -c -p -v Main
// truncated
// added new lines for brevity
BootstrapMethods:
  0: #55 REF_invokeStatic java/lang/invoke/LambdaMetafactory.metafactory:
    (Ljava/lang/invoke/MethodHandles$Lookup;
     Ljava/lang/String;
     Ljava/lang/invoke/MethodType;
     Ljava/lang/invoke/MethodType;
     Ljava/lang/invoke/MethodHandle;
     Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
    Method arguments:
      #62 (Ljava/lang/Object;)Z
      #64 REF_invokeStatic Main.lambda$main$0:(Ljava/lang/String;)Z
      #67 (Ljava/lang/String;)Z

　　

注意bootstrap返回的是ConstantCallSite。此外，java还提供了MutableCallSite和VolatileCallSite功能，也能实现类似逻辑。

9. JDBC: 提供了RowSetFactory, RowSetProvider, RowSet,CachedRowSet, JdbcRowSet等。

import javax.sql.rowset.JdbcRowSet;  
import javax.sql.rowset.RowSetProvider;    
class JdbcExample{    
    public staticvoid main(String args[]) throws Exception{  
        try(// --------------try-with-resources begin-------------//  
            // Creating connection  
            JdbcRowSet jRS = RowSetProvider.newFactory().createJdbcRowSet();  
           )// --------------try-with-resources end--------------//  
        { // ----------------try block begin---------------------//  
            // Set database connection  
            jRS.setUrl("jdbc:mysql://localhost:3306/student");  
            // Set database username  
            jRS.setUsername("root");  
            // Set database password  
            jRS.setPassword("mysql");  
            // Set sql query to execute   
            jRS.setCommand("select * from user");  
            // Execute query  
            jRS.execute();  
            // Getting 3rd row because it is scrollable by default  
            jRS.absolute(3);    
            System.out.println(jRS.getInt(1)+""+jRS.getString(2)+""+jRS.getString(3));    
            // Updating 3rd row  
            jRS.updateString("name", "Neraj Kumar Singh");  
            jRS.updateRow();  
            // Fetching 3rd row again  
            System.out.println(jRS.getInt(1)+""+jRS.getString(2)+""+jRS.getString(3));  

            // Set sql query to execute   
            jRS.setCommand("select * from user");  
            // Execute query  
            jRS.execute();  
            while(jRS.next()){    
                System.out.println(jRS.getInt(1)+""+jRS.getString(2)+""+jRS.getString(3));    
            }      
        } // ----------------try block end----------------------//  
        catch(Exception e){ // Exception handler   
            System.out.println(e);  
        }    
    }  
}  

Java 8

 1. lambda expression，基本结构(args)->{dosth;return sth2;}

例子来自javatpoint.com

Sayable s2= name ->{  
            return "Hello, "+name;  
        };  

  Addable ad2=(int a,int b)->(a+b);  

　　

list.forEach(  
    (n)->System.out.println(n)  
); 

　　

        Runnable r2=()->{  
                System.out.println("Thread2 is running...");  
        };  
        Thread t2=new Thread(r2);  
        t2.start();  

　　

        Collections.sort(list,(p1,p2)->{  
        return p1.name.compareTo(p2.name);  
        }); 

　　

Stream<Product> filtered_data = list.stream().filter(p -> p.price > 20000);  

　　

b.addActionListener(e-> {tf.setText("hello swing");});  

　　

2. Method Reference

 a) Reference to a Static Method：基本语法Class::staticMethod

例如，可以定义一个functional interface，然后把一个参数构成相同的静态方法引用为该interface实例。

interface Sayable{  
    void say();  
}  
public class MethodReference {  
    public static void saySomething(){  
        System.out.println("Hello, this is static method.");  
    }  
    public static void main(String[] args) {  
        // Referring static method  
        Sayable sayable = MethodReference::saySomething;  
        // Calling interface method  
        sayable.say();  //Hello, this is static method.
    }  
}  

以下实例则直接将静态方法转化为Runnable接口：

public class MethodReference2 {  
    public static void ThreadStatus(){  
        System.out.println("Thread is running...");  
    }  
    public static void main(String[] args) {  
        Thread t2=new Thread(MethodReference2::ThreadStatus);  
        t2.start();       
    }  
}  

　　

还能用静态方法来override另一个类中的静态方法。

import java.util.function.BiFunction;  
class Arithmetic{  
public static int add(int a, int b){  
return a+b;  
}  
public static float add(int a, float b){  
return a+b;  
}  
public static float add(float a, float b){  
return a+b;  
}  
}  
public class MethodReference4 {  
public static void main(String[] args) {  
BiFunction<Integer, Integer, Integer>adder1 = Arithmetic::add;  
BiFunction<Integer, Float, Float>adder2 = Arithmetic::add;  
BiFunction<Float, Float, Float>adder3 = Arithmetic::add;  
int result1 = adder1.apply(10, 20);  
float result2 = adder2.apply(10, 20.0f);  
float result3 = adder3.apply(10.0f, 20.0f);  
System.out.println(result1);  
System.out.println(result2);  
System.out.println(result3);  
}  
}

b) Ref to an instance method: obj::methodname

public class InstanceMethodReference2 {  
    public void printnMsg(){  
        System.out.println("Hello, this is instance method");  
    }  
    public static void main(String[] args) {  
    Thread t2=new Thread(new InstanceMethodReference2()::printnMsg);  
        t2.start();       
    }  
}  

c) Ref to a Constructor: class::new

interface Messageable{  
    Message getMessage(String msg);  
}  
class Message{  
    Message(String msg){  
        System.out.print(msg);  
    }  
}  
public class ConstructorReference {  
    public static void main(String[] args) {  
        Messageable hello = Message::new;  
        hello.getMessage("Hello");  
    }  
}  

3. 下划线变成了keyword，不能再直接用来当变量名了。

4. 提供了defaultStream和staticStream两个类。提供了takeWhile, dropWhile。

import java.util.List;  
import java.util.stream.Collectors;  
import java.util.stream.Stream;  
public class StreamExample {  
    public static void main(String[] args) {  
        List<Integer> list   
        = Stream.of(2,2,3,4,5,6,7,8,9,10)  
                .takeWhile(i -> (i % 2 == 0)).collect(Collectors.toList());     
    System.out.println(list);  //[2,2]
    }  
}  

　　

dropwhile类似。

创建时也有两个值得一提的方法-ofNullable和iterate。

ofNullable，也就是Stream.of，当传入的是null的时候，返回empty stream，更方便处理null stream和NullPointerException。Stream<Integer> val = Stream.ofNullable(null);    

iterate(seed; hasNext;next)

import java.util.stream.Stream;  
  
public class StreamExample {  
    public static void main(String[] args) {  
        Stream.iterate(1, i -> i <= 10, i -> i*3)  
        .forEach(System.out::println);  
    }  
}  

　　

5. 引入Module，用来管理多个package。能够生成Modular JAR。这个JAR会包含一个用来描述信息的module-info.class。此外，还能生成JMOD格式，这个格式与JAR相似，但是能够包含源代码和config文件。

 module-info.java的内容示例：

module com.javatpoint{  
  
}  

　

编译: javac -d mods --module-source-path src/ --module com.javatpoint  

运行: java --module-path mods/ --module com.javatpoint/com.javatpoint.Hello  

6. 引入JShell

7. 新的version命名格式: $MAJOR.$MINOR.$SECURITY.$PATCH

8. try-with-resource升级，现在可以在外面定义好：

import java.io.FileNotFoundException;  
import java.io.FileOutputStream;  
public class FinalVariable {  
    public static void main(String[] args) throws FileNotFoundException {  
        FileOutputStream fileStream=new FileOutputStream("javatpoint.txt");  
        try(fileStream){  
             String greeting = "Welcome to javaTpoint.";      
                byte b[] = greeting.getBytes();       
                fileStream.write(b);      
                System.out.println("File written");           
        }catch(Exception e) {  
            System.out.println(e);  
        }         
    }  
} 

　　

9. Process API改进，例如：

public class ProcessApiExample {  
    public static void main(String[] args) {  
        ProcessHandle currentProcess = ProcessHandle.current();     // Current processhandle  
        System.out.println("Process Id: "+currentProcess.pid());    // Process id   
        System.out.println("Direct children: "+ currentProcess.children()); // Direct children of the process  
        System.out.println("Class name: "+currentProcess.getClass());       // Class name  
        System.out.println("All processes: "+ProcessHandle.allProcesses()); // All current processes   
        System.out.println("Process info: "+currentProcess.info());         // Process info  
        System.out.println("Is process alive: "+currentProcess.isAlive());   
        System.out.println("Process's parent "+currentProcess.parent());  // Parent of the process  
    }  
}

　　

10. List, Set, Map都能够使用Java9的静态工厂类方法来创建，比如：

import java.util.Map;  
public class FactoryMethodsExample {  
    public static void main(String[] args) {  
        Map<Integer,String> map = Map.of(101,"JavaFX",102,"Hibernate",103,"Spring MVC");  
        for(Map.Entry<Integer, String> m : map.entrySet()){    
            System.out.println(m.getKey()+" "+m.getValue());  
        }  
    }  
} 

　　

import java.util.Set;  
public class FactoryMethodsExample {  
    public static void main(String[] args) {  
        Set<String> set = Set.of("Java","JavaFX","Spring","Hibernate","JSP");  
        for(String l:set) {  
            System.out.println(l);  
        }  
    }  
} 

　　

11. @SafeVarargs  

12. 允许在接口中创建private方法。

interface Sayable{  
    default void say() {  
        saySomething();  
    }  
    // Private method inside interface  
    private void saySomething() {  
        System.out.println("Hello... I'm private method");  
    }  
}  
public class PrivateInterface implements Sayable {  
    public static void main(String[] args) {  
        Sayable s = new PrivateInterface();  
        s.say();  
    }  
}  

　　

13. Anonymous Inner Class创建也能自动推测泛型。

abstract class ABCD<T>{  
    abstract T show(T a, T b);  
}  
public class TypeInferExample {  
    public static void main(String[] args) {  
        ABCD<String> a = new ABCD<>() { // diamond operator is empty  
            String show(String a, String b) {  
                return a+b;   
            }  
        };    
        String result = a.show("Java","9");  
        System.out.println(result);  
    }  
}  

　　

Java 10

1. 局部变量类型推断升级

var list = new ArrayList<String>(); // ArrayList<String>
var stream = list.stream(); // Stream<String>

　　

2. 整合JDK代码仓库

3. 统一GC接口，为 G1 引入多线程并行 GC

4. 增加了Application Class-Data Sharing，允许将应用类放置在共享存档中，能够让服务快速启动改善系统响应时间。

5. Thread-Local Handshakes， 能够单独对某个JVM线程操作-允许在不运行全局JVM安全点的情况下实现线程回调，由线程本身或者JVM线程来执行，同时保持线程处于阻塞状态，这种方式使得停止单个线程变成可能

6. 变更命名机制: $FEATURE.$INTERIM.$UPDATE.$PATCH

7. 提供默认的根证书认证

8. 实验性质的JIT编译器Graal。-XX：+ UnlockExperimentalVMOptions -XX：+ UseJVMCICompiler

9. 拓展了Unicode

java.text.DateFormat::get*Instance
java.text.DateFormatSymbols::getInstance
java.text.DecimalFormatSymbols::getInstance
java.text.NumberFormat::get*Instance
java.time.format.DateTimeFormatter::localizedBy
java.time.format.DateTimeFormatterBuilder::getLocalizedDateTimePattern
java.time.format.DecimalStyle::of
java.time.temporal.WeekFields::of
java.util.Calendar::{getFirstDayOfWeek,getMinimalDaysInWeek}
java.util.Currency::getInstance
java.util.Locale::getDisplayName
java.util.spi.LocaleNameProvider

10 .Heap Allocation on Alternative Memory Devices 

11. Optional

Optional<String> name = Optional.ofNullable(str); // New API added - is preferred option then get() method name.orElseThrow();

 

Java 11

1. 为lambda参数的类型推断

Function<String, String> append = (var string) -> string + " ";

　　

2. String::lines

multiline.lines()

    // we now have a `Stream<String>`

    .map(line -> "// " + line)

    .forEach(System.out::println);

　　

3.  新字符

4. Standard HTTP Client-jdk.incubator.http

5. File的新方法: ‘writeString()’, ‘readString()’ and ‘isSameFile()’. ‘writeString()’ 

6.  ‘-XX: +UseDynamicNumberOfCompilerThreads.’  动态分配编译器线程，每个type只产生一个thread

7. Z garbage Collector: 保证停顿不会超过10ms

8. jceks.key.serialFilte

9. Low-overhead Heap Profiling

10. Epsilon Garbage Collector: 用于处理没有实现任何内存回收机制的分配的内存

11. .toArray(IntFunction)