经过学习总结:
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　　1.String本身是不具备比较大小功能的,但是由于String对象实现了
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　　Comparable的接口.这个接口是可比较功能的接口.这里定义了比较方法compareTo方法.
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　　Api手册中的描述:
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　　此接口强行对实现它的每个类的对象进行整体排序。
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　　这种排序被称为类的自然排序，类的 compareTo 方法被称为它的自然比较方法(Through the study summary:
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1.String itself does not have the size function, but because the String object has been implemented
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The interface of Comparable. This interface is the interface of comparable functions. The comparison method compareTo method is defined here
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Descr iption in the Api manual:
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This interface forces an overall ordering of objects that implement each of its classes.
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This sort is called the natural ordering of classes, and the class of compareTo methods is called its natural comparison method)