使用toString打印出ArrayList [英] Printing out ArrayList with toString

问题描述

当我创建一个ArrayList对象并向其添加其他对象时，打印出ArrayList对象将打印出内部对象的内存引用.但是，如果我将String添加到ArrayList对象，它将不会打印出String的内存引用，而是打印出实际的String值.字符串也是类权限的对象，那么为什么不打印出字符串内存引用呢?

When I create an ArrayList object and add other objects to it, printing out the ArrayList object will print out the memory references of the objects inside. However, if I add String to the ArrayList object, it will not print out the memory references of the String but rather the actual String value. String is also an object of a class right, so why does it not print out the String memory reference?

推荐答案

Java中Collection的toString方法(这是ArrayList扩展的内容)在其每个元素上使用String.valueOf: http://docs.oracle.com/javase/7/docs/api/java/util/AbstractCollection.html#toString()

The toString method for a Collection in Java (which is what an ArrayList extends) uses String.valueOf on each of its elements: http://docs.oracle.com/javase/7/docs/api/java/util/AbstractCollection.html#toString()

字符串表示形式由集合的元素的列表组成，这些元素按其迭代器返回的顺序排列，并括在方括号("[]")中.相邻元素由字符，"(逗号和空格)分隔.元素由String.valueOf(Object)转换为字符串.

String.valueOf只是获取对象的toString值:

String.valueOf is simply grabbing the toString value of the object: http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#valueOf(java.lang.Object)

如果参数为null，则字符串等于"null"；否则，将返回obj.toString()的值.

if the argument is null, then a string equal to "null"; otherwise, the value of obj.toString() is returned.

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