groovy demos

groovy_demo

public class GroovyTest {
    // sum method
    def static sum(n, closure) {
      for(int i = 2; i <= n; i += 2) {
        closure(i)
      }
      // return 2
      2
    }
    
    def static paramsDemo(a, b, c, closure) {
        closure(a + b + c, a + b)
    }
    
    public static void main(String []args){
        println "java in groovy!"
        for(int i =  0;i < 10;i++) {
            System.out.print(i);
            print i + ","
        }
        println "\nrange for";
        for (i in 0..2) {
            print i
        }
        println "\nclosure"
        0.upto(10){
            print "$it"
        }
        println  "\nrepeat "
        3.times {
            print "index $it,"
            print "ho "
        }
        println "\nstep demo"
        1.step(10, 5) {
            print "$it,"
        }
        println "\nsystem command invocation!"
        print "java -version".execute().text;

        println "\na new way to check null"
        String a = null
        a?.print()

        println "\ncatch exception is not necessary!"
        println "semicolon is not necessary!"
       
        // evaluate expression in string
        println "${1==0}"


        def total = 1
        // 666
        println "${sum(10, {index -> println "$index";total *= index})}"
        println total
        
        sum(10){index -> total *= index}
        println total
        
        paramsDemo("hello ", "world", "!") {
            cb1, cb2 -> println cb1 + cb2
        }
  }
}