Groovy tries to be as natural as possible for Java developers. Here are all the major
differences between Java and Groovy.
-Default imports
In Groovy all these packages and classes are imported by default, i.e. Developers 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.*
-Multi-methods
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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.
-Array initializers
In Groovy, the { … } block is reserved for closures. That means that you cannot create
array literals with this syntax:
int[] arraySyntex = { 6, 3, 1}
You actually have to use:
int[] arraySyntex = [1,2,3]
-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.
-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.
-String and Character literals
Singly-quoted literals in Groovy are used for String , and double-quoted result
in String or GString , depending whether there is interpolation in the literal.
assert 'c'.getClass()==String
assert "c".getClass()==String
assert "c${1}".getClass() in GString
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
