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63 当心字符串连接的性能问题不要使用字符串连接操作符合并多个字符串字符串连接操作符(+) 是将几个字符串组合成一个字符串的简便方法。为了连接n个字符而重复地使用字符串连接操作符，需要O(n^2)的时间。因为字符串是不可变的，当两个字符串被连接在一起时，它们的内容都要被拷贝。例如，下面代码将每个账单...

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57 最小化局部变量的作用域要使局部变量的作用域最小化，最好的方法是在首次使用的地方声明它。过早地声明局部变量可能导致其作用域不仅过早开始而且结束太晚。每个局部变量声明都应该包含一个初始化表达式。这个规则的一个例外是try-catch语句。如果该值必须在try块之外使用，那么它必须在try块之前声明...

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