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

问题描述

当我创建一个 ArrayList 对象并向其中添加其他对象时，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，它不会打印出 String 的内存引用，而是打印出实际的 String 值.String也是一个类的对象吧，为什么不打印出String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(这就是 ArrayListcode> extends) 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()

字符串表示由集合元素的列表组成，按其迭代器返回的顺序排列，括在方括号([]")中.相邻元素由字符,"(逗号和空格)分隔.元素通过 String.valueOf(Object) 转换为字符串.

The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(Object).

String.valueOf 只是获取对象的 toString 值:http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#valueOf(java.lang.Object)

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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