Boolean expressions
Groovy支持标准的条件运算符的布尔表达式：
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def a = true |
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def b = true |
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def c = false |
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assert a |
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assert a && b |
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assert a || c |
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assert !c |
此外，Groovy中有强制转换非布尔对象为布尔值的特殊规则。
集合
空集合会被强制转换为false：
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def numbers = [1,2,3] |
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assert numbers //true, as numbers in not empty |
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numbers = [] |
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assert !numbers //true, as numbers is now an empty collection |
迭代器和枚举
没有进一步元素的枚举和迭代器都会被强制转换为false：
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assert ![].iterator() // false because the Iterator is empty |
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assert [0].iterator() // true because the Iterator has a next element |
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def v = new Vector() |
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assert !v.elements() // false because the Enumeration is empty |
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v.add(new Object()) |
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assert v.elements() // true because the Enumeration has more elements |
Map
非空的map被强制转换为true：
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assert ['one':1] |
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assert ![:] |
Matchers
当匹配到正则表达式的模式的时候会强制转换为true:
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assert ('Hello World' =~ /World/) //true because matcher has at least one match |
Strings
非空的Strings, GStrings 和CharSequences 将被强制转换为true：
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<div> |
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<div> |
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<pre><code data-result="[object Object]">// Strings |
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assert 'This is true' |
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assert !'' |
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//GStrings |
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def s = '' |
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assert !("$s") |
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s = 'x' |
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assert ("$s") |
Numbers
非0的数值被强制转换为true，就如同perl一样。
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<div> |
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<div> |
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<pre><code data-result="[object Object]">assert !0 //yeah, 0s are false, like in Perl |
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assert 1 //this is also true for all other number types |
Object references
非null的对象引用被强制转换为true：
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assert new Object() |
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assert !null |