null强转机制

对于Object,null强转是安全的

class LangTest extends Specification {
    def "null cast obj is safe"() {
        when:
        Object a = null
        Integer obj = a
        then:
        obj == null
    }

    def "null cast primitive error"() {
        when:
        Object a = null
        //抛出异常的原因是隐式调用了Integer.intValue(),而a为空
        int primitive = (Integer) a
        then:
        def ex = thrown(NullPointerException)
        ex.class.name == "java.lang.NullPointerException"
    }
}

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使用groovy+spock进行单元测试 https://www.cnblogs.com/lovesqcc/p/8647201.html