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the differences between groovy and java

发布时间：2020-12-14 16:41:21 所属栏目：大数据 来源：网络整理
导读：Groovy tries to be as natural as possible for Java developers. We’ve tried to follow the principle of least surprise when designing Groovy,particularly for developers learning Groovy who’ve come from a Java background. Here we list all t

Groovy tries to be as natural as possible for Java developers. We’ve tried to follow the principle of least surprise when designing Groovy,particularly for developers learning Groovy who’ve come from a Java background.

Here we list all the major differences between Java and Groovy.

1. Default imports

All these packages and classes are imported by default,i.e. you do not have to use an explicit?import?statement to use them:

  • java.io.*

  • java.lang.*

  • java.math.BigDecimal

  • java.math.BigInteger

  • java.net.*

  • java.util.*

  • groovy.lang.*

  • groovy.util.*

2. Multi-methods

In Groovy,the methods which will be invoked are chosen at runtime. This is called runtime dispatch or multi-methods. It means that the method will be chosen based on the types of the arguments at runtime. In Java,this is the opposite: methods are chosen at compile time,based on the declared types.

The following code,written as Java code,can be compiled in both Java and Groovy,but it will behave differently:

int method(String arg) { return 1;}Object2  o = "Object" result (o);

In Java,you would have:

assertEquals(, result);

Whereas in Groovy:

o?is declared as an?Object,whereas Groovy will choose at runtime,when the method is actually called. Since it is called with a?String,then the?String?version is called.

3. Array initializers

In Groovy,the?{ …? }?block is reserved for closures. That means that you cannot create array literals with this syntax:

[]

4. Package scope visibility

In Groovy,omitting a modifier on a field doesn’t result in a package-private field like in Java:

@PackageScope:
 
  
 
 
 5. ARM blocks
 
 
 
  
 
   
ARM (Automatic Resource Management) block from Java 7 are not supported in Groovy. Instead,Groovy provides various methods relying on closures,which have the same effect while being more idiomatic. For example:
 
  
 
  
 
   
 
    
Path file Paths.get("/path/to/file");Charset charset CharsetforName"UTF-8"tryBufferedReader reader FilesnewBufferedReaderfile charset)) linewhile((line  readerreadLine())!=nullSystemoutprintlnlinecatchIOException eprintStackTrace();}
 
   
 
  
 
  
 
   
can be written like this:
 
  
 
  
 
   
 
    
).eachLine'UTF-8' println it }
 
   
 
  
 
  
 
   
or,if you want a version closer to Java:
 
  
 
  
 
   
 
    
 
 
 6. Inner classes
 
 
 
  
 
   

 
      The implementation of anonymous inner classes and nested classes follows the Java lead,but you should not take out the Java Language Spec and keep shaking the head about things that are different. The implementation done looks much like what we do for?groovy.lang.Closure,with some benefits and some differences. Accessing private fields and methods for example can become a problem,but on the other hand local variables don’t have to be final. 
     


 
  
 
   
 6.1. Static inner classes
 
   
 
    
Here’s an example of static inner class:
 
   
 
   
 
    
 
     
import javautilconcurrent.CountDownLatchTimeUnit called CountDownLatchTimer timer Timer() timerschedule(TimerTaskvoid run calledcountDown},102)">0assertawait10TimeUnitSECONDS)
 
    
 
   
 
  
 
  
 
   
 6.3. Creating Instances of Non-Static Inner Classes
 
   
 
    
In Java you can do this:
 
   
 
   
 
    
 
     
y.new X()?syntax. Instead,you have to write?new X(y),like in the code below:
 
   
 
   
 
    
 
     
 
 
 7. Lambdas
 
 
 
  
 
   
Java 8 supports lambdas and method references:
 
  
 
  
 
   
 
    
 println 'run'each  // or list.each(this.&println)
 
   
 
  
 
 
 

 

 
 
 8. GStrings
 
 
 
  
 
   
As double-quoted string literals are interpreted as?GString?values,Groovy may fail with compile error or produce subtly different code if a class with?String?literal containing a dollar character is compiled with Groovy and Java compiler.
 
  
 
  
 
   
While typically,Groovy will auto-cast between?GString?and?String?if an API declares the type of a parameter,beware of Java APIs that accept an?Object?parameter and then check the actual type.
 
  
 
 
 

 

 
 
 9. String and Character literals
 
 
 
  
 
   
Singly-quoted literals in Groovy are used for?String?or?GString,depending whether there is interpolation in the literal.
 
  
 
  
 
   
 
    
getClass()=="c""c${1}"inGString
 
   
 
  
 
  
 
   
Groovy will automatically cast a single-character?String?to?char?only when assigning to a variable of type?char. When calling methods with arguments of type?char?we need to either cast explicitly or make sure the value has been cast in advance.
 
  
 
  
 
   
 
    
Characterdigita16)==10:'But Groovy does boxing'((char'a'false'Need explicit cast'catchMissingMethodException}
 
   
 
  
 
  
 
   
Groovy supports two styles of casting and in the case of casting to?char?there are subtle differences when casting a multi-char strings. The Groovy style cast is more lenient and will take the first character,while the C-style cast will fail with exception.
 
  
 
  
 
   
 
    
// for single char strings,both are the same).class==Character"c"as// for multi char strings they are not'cx'=='c''will fail - not castable'GroovyCastException'cx'asType'c'
 
   
 
  
 
 
 

 

 
 
 10. Primitives and wrappers
 
 
 
  
 
   
Because Groovy uses Objects for everything,it?autowraps?references to primitives. Because of this,it does not follow Java’s behavior of widening taking priority over boxing. Here’s an example using?int
 
  
 
  
 
   
 
    
 
 
 11. Behaviour of?==

 
 
 
  
 
   
In Java?==?means equality of primitive types or identity for objects. In Groovy?==?translates to?a.compareTo(b)==0,if they are?Comparable,and?a.equals(b)?otherwise. To check for identity,there is?is. E.g.?a.is(b).
 
  
 
 
 

 

 
 
 12. Conversions
 
 
 
  
 
   
Java does automatic widening and narrowing?conversions.
 
  
 
  


     Table 1. Java Conversions 
    
   













? 
      
      
 
       
 
        
Converts to
 
       
 
      
 		 
    



 
Converts from
 		 
      
      
 
       
 
        
boolean
 
       
 
      
 		 
      
      
 
       
 
        
byte
 
       
 
      
 		 
      
      
 
       
 
        
short
 
       
 
      
 		 
      
      
 
       
 
        
char
 
       
 
      
 		 
      
      
 
       
 
        
int
 
       
 
      
 		 
      
      
 
       
 
        
long
 
       
 
      
 		 
      
      
 
       
 
        
float
 
       
 
      
 		 
      
      
 
       
 
        
double
 
       
 
      
 		 
    



 
boolean
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
    



 
byte
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
short
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
char
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
int
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
long
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
    



 
float
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
double
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
C
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
    





 
   
*?'Y' indicates a conversion Java can make,'C' indicates a conversion Java can make when there is an explicit cast,'T` indicates a conversion Java can make but data is truncated,'N' indicates a conversion Java can’t make.
 
  
 
  
 
   
Groovy expands greatly on this.
 
  
 
  


     Table 2. Groovy Conversions 
    
   























? 
      
      
 
       
 
        
Converts to
 
       
 
      
 		 
    



 
Converts from
 		 
      
      
 
       
 
        
boolean
 
       
 
      
 		 
      
      
 
       
 
        
Boolean
 
       
 
      
 		 
      
      
 
       
 
        
byte
 
       
 
      
 		 
      
      
 
       
 
        
Byte
 
       
 
      
 		 
      
      
 
       
 
        
short
 
       
 
      
 		 
      
      
 
       
 
        
Short
 
       
 
      
 		 
      
      
 
       
 
        
char
 
       
 
      
 		 
      
      
 
       
 
        
Character
 
       
 
      
 		 
      
      
 
       
 
        
int
 
       
 
      
 		 
      
      
 
       
 
        
Integer
 
       
 
      
 		 
      
      
 
       
 
        
long
 
       
 
      
 		 
      
      
 
       
 
        
Long
 
       
 
      
 		 
      
      
 
       
 
        
BigInteger
 
       
 
      
 		 
      
      
 
       
 
        
float
 
       
 
      
 		 
      
      
 
       
 
        
Float
 
       
 
      
 		 
      
      
 
       
 
        
double
 
       
 
      
 		 
      
      
 
       
 
        
Double
 
       
 
      
 		 
      
      
 
       
 
        
BigDecimal
 
       
 
      
 		 
    



 
boolean
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
    



 
Boolean
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
      
      
 
       
 
        
N
 
       
 
      
 		 
    



 
byte
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
Byte
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
short
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
Short
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
char
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
    



 
Character
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
    



 
int
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
Integer
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
long
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
Long
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
BigInteger
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
    



 
float
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
Float
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
double
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
Double
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
B
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
      
      
 
       
 
        
Y
 
       
 
      
 		 
    



 
BigDecimal
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
T
 
       
 
      
 		 
      
      
 
       
 
        
D
 
       
 
      
 		 
      
      
 
       
 
        
-
 
       
 
      
 		 
    





 
   
*?'Y' indicates a conversion Groovy can make,'D' indicates a conversion Groovy can make when compiled dynamically or explicitly cast,'T` indicates a conversion Groovy can make but data is truncated,'B' indicates a boxing/unboxing operation,'N' indicates a conversion Groovy can’t make.
 
  
 
  
 
   
The truncation uses?Groovy Truth?when converting to?boolean/Boolean. Converting from a number to a character casts the?Number.intvalue()?to?char. Groovy constructs?BigInteger?and?BigDecimal?using?Number.doubleValue()?when converting from a?Float?or?Double,otherwise it constructs using?toString(). Other conversions have their behavior defined by?java.lang.Number.
 
  
 
 
 

 

 
 
 13. Extra keywords
 
 
 
  
 
   
There are a few more keywords in Groovy than in Java. Don’t use them for variable names etc.
 
  
 
  
 
   
    

  •  
    as
     
    •  
    
  •  
    def
     
    •  
    
  •  
    in
     
    •  
    
  •  
    trait
     
    •  
   


 
 
 


        

            

        	




                        
（编辑：李大同）


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