Groovy （三） 闭包的使用-----极速入门总结

一、直接摆例子

/**
 * Created by Administrator on 2016/8/6.
 */
/**
* 闭包的使用
* 避免了代码的冗长，可以辅助创建轻量级可复用的代码片段
*/
print("\n闭包的使用:")
def pickEven(n, block) {
    for (int i = 2; i <= n; i += 2) {
        block(i)
    }
    println()
}

pickEven(6, { print it })
pickEven(6) { eventNum -> print eventNum }

def totalSelectValues(n, closure) {
    total = 0
    for (i in 1..n) {
        if (closure(i)) {
            total += i
        }
    }
    total//没有显示的return 则返回最后一个
}

def isOdd = { it % 2 != 0 }
println totalSelectValues(10, isOdd)

/**
 * 闭包的作用范围:只有在闭包被定义且存在，而不是在被调用时可以访问其状态值
 */
println("\n闭包的作用范围:")
def greeting ='Hello'
def clos ={param -> println "${greeting} ${param}"}
clos.call("world")

greeting ='Welcome'
clos.call('Ken')

def demo(clo){
    def greeting = 'Bonjour'
    clo.call('Ken')
}
demo(clos)

/**
 * 闭包在实参列表外部
 */
 greeting ='Hello'
 clos ={param -> println "${greeting} ${param}"}
 demo(clo){
     greeting = 'Bonjour'
    clo.call('Ken')
}
//demo() clos //报错
demo() {param -> println "${greeting} ${param}"}
demo clos
demo {param -> println "${greeting} ${param}"}
/**
 * 向闭包传递参数
 * 对于单参数，it是该参数的默认名称
 * 如果多余一个参数，就得一一列出
 */
println("\n向闭包传递参数:")
def tellFortune(closure) {
    closure new Date("09/20/2016"), "your day!!"
}

tellFortune() {
    date, fortune -> println "Fortune for $date id $fortune"
}


/**
 *  update 的用法
 */

def iterate(n, closure) {
    1.upto(n) {
        println "in iterate with value n is ${it}"
        closure(it)
    }
}

total = 0
closure = {
    total += it// 每次调用闭包，都会恢复到上一次的total值
    println "in closure value total is ${total}"
}
iterate(4, closure)

/**
 * curry 闭包
 * 在多次调用同一个闭包的时候，有一个或者多个实参是相同的，传参就会很枯燥
 * 可以预先绑定某个形参，调用闭包的时候就不必重复为这个闭包提供参数了
 */

def tellFortunes(closure) {
    Date date = new Date("09/20/2016")
//    closure date,"first"
//    closure date,"second"
    //postForturn 保存着保存着科里化后的闭包引用，已经绑定了date数据
    postFortune = closure.curry(date)
    postFortune "first"
    postFortune "second"
}

tellFortunes() {
    date, forturn ->
        println "Fortunes for ${date} is ${forturn}"
}

/**
 * 动态闭包
 *  1根据闭包是否参在
 *  2参数数目closure.maximumNumberOfParameters
 *  3参数类型closure.paremeterTypes
 */
def doSomething(closure) {
    if (closure) {
        closure()
    } else {
        println "Using default"
    }
}

doSomething()
doSomething() { println "doSomething with closure" }



/**
 * 使用尾递归编写程序
 * 递归程序转换成迭代过程，提高性能
 *
 * */
def factorial
factorial = { int number, int theFcatorial ->
    number == 1 ? theFcatorial : factorial.trampoline(number - 1, number * theFcatorial)
}.trampoline()

println "factorial 5 value is ${factorial(5, 1)}"