Basic programming snippets in Groovy -Java Village

Before going to start with snippets, just wanted to tell you that Grrovy is scripting language for Java, Can make more dynamic. Comparing with Java, more similarities even in coding side also. will try to cover some areas in Groovy.

If we know Java and Javascript can easily understand Groovy.

Variable creation
Here no need to specify type for variable like javascript

def x = false
def y = 5

if - else statement
Groovy supports the usual if - else syntax from Java.

def x = false
def y = false

if ( !x ) {
    x = true
}

assert x == true

if ( x ) {
    x = false
} else {
    y = true
}

assert x == y

Groovy also supports the normal Java "nested" if then else if syntax

Ternary operator
Groovy also supports the ternary operator:

def y = 5
def x = (y > 1) ? "worked" : "failed"
assert x == "worked"

Switch statement
The switch statement in Groovy is backwards compatible with Java code; so you can fall through cases sharing the same code for multiple matches. One difference though is that the Groovy switch statement can handle any kind of switch value and different kinds of matching can be performed.

def x = 1.23
def result = ""

switch ( x ) {
    case "foo":
        result = "found foo"
        // lets fall through

    case "bar":
        result += "bar"

    case [4, 5, 6, 'inList']:
        result = "list"
        break

    case 12..30:
        result = "range"
        break

    case Integer:
        result = "integer"
        break

    case Number:
        result = "number"
        break

    default:
        result = "default"
}

assert result == "number"

Looping
Groovy supports the usual while {...} and for loops like Java.

def x = 0
def y = 5

while ( y-- > 0 ) {
    x++
}

assert x == 5

// iterate over a range
def x = 0
for ( i in 0..9 ) {
    x += i
}
assert x == 45

// iterate over a list
x = 0
for ( i in [0, 1, 2, 3, 4] ) {
    x += i
}
assert x == 10

// iterate over an array
array = (0..4).toArray()
x = 0
for ( i in array ) {
    x += i
}
assert x == 10

// iterate over a map
def map = ['abc':1, 'def':2, 'xyz':3]
x = 0
for ( e in map ) {
    x += e.value
}
assert x == 6

// iterate over values in a map
x = 0
for ( v in map.values() ) {
    x += v
}
assert x == 6

// iterate over the characters in a string
def text = "abc"
def list = []
for (c in text) {
    list.add(c)
}
assert list == ["a", "b", "c"]

Closures
In addition, you can use closures in place of most for loops, using each() and eachWithIndex():

def stringList = [ "java", "perl", "python", "ruby", "c#", "cobol",
                   "groovy", "jython", "smalltalk", "prolog", "m", "yacc" ];

def stringMap = [ "Su" : "Sunday", "Mo" : "Monday", "Tu" : "Tuesday",
                  "We" : "Wednesday", "Th" : "Thursday", "Fr" : "Friday",
                  "Sa" : "Saturday" ];

stringList.each() { print " ${it}" }; println "";


stringMap.each() { key, value -> println "${key} == ${value}" };
// Su == Sunday
// We == Wednesday
// Mo == Monday
// Sa == Saturday
// Th == Thursday
// Tu == Tuesday
// Fr == Friday

stringList.eachWithIndex() { obj, i -> println " ${i}: ${obj}" };

try-catch blocks
For try/catch/finally blocks, the last expression evaluated is the one being returned. If an exception is thrown in the try block, the last expression in the catch block is returned instead. Note that finally blocks don't return any value.

def method(bool) {
    try {
        if (bool) throw new Exception("foo")
        1
    } catch(e) {
        2
    } finally {
        3
    }
}

assert method(false) == 1
assert method(true) == 2

Operator Overloading
Groovy supports operator overloading which makes working with Numbers, Collections, Maps and various other data structures easier to use.
Various operators in Groovy are mapped onto regular Java method calls on objects.
This allows you the developer to provide your own Java or Groovy objects which can take advantage of operator overloading. The following table describes the operators supported in Groovy and the methods they map to.

Operator	Method
a + b	a.plus(b)
a - b	a.minus(b)
a * b	a.multiply(b)
a ** b	a.power(b)
a / b	a.div(b)
a % b	a.mod(b)
a \| b	a.or(b)
a & b	a.and(b)
a ^ b	a.xor(b)
a++ or ++a	a.next()
a-- or --a	a.previous()
a[b]	a.getAt(b)
a[b] = c	a.putAt(b, c)
a << b	a.leftShift(b)
a >> b	a.rightShift(b)
switch(a) { case(b) : }	b.isCase(a)
~a	a.bitwiseNegate()
-a	a.negative()
+a	a.positive()

Note that all the following comparison operators handle nulls gracefully avoiding the throwing of java.lang.NullPointerException.

Operator	Method
a == b	a.equals(b) or a.compareTo(b) == 0 **
a != b	! a.equals(b)
a <=> b	a.compareTo(b)
a > b	a.compareTo(b) > 0
a >= b	a.compareTo(b) >= 0
a < b	a.compareTo(b) < 0
a <= b	a.compareTo(b) <= 0