blocks|key|1521381|text|对集合调用toString应返回一个包含所有元素字符串表示形式的字符串。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1521382|这不适用于内置数组，因为它们没有toString覆盖，只会给你一个内存地址。|1521383|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Calling toString on the collection should return a string containing all the elements string representations.

This won't work with built-in arrays though, as they don't have a toString override and will just give you a memory address.

blocks|key|1521834|text|根据您到底想做什么，解决方案可能相当简单。下面的代码不会生成print_r提供的格式化输出，但允许您输出列表、数组和映射的结构：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1521835|++++//+Output+a+list
++++final+List<String>+list+=+new+ArrayList<String>();
++++list.add("one");
++++list.add("two");
++++list.add("three");
++++list.add("four");
++++System.out.println(list);

++++//+Output+an+array
++++final+String[]+array+=+{"four",+"three",+"two",+"one"};
++++System.out.println(Arrays.asList(array));

++++//+Output+a+map
++++final+Map<String,+String>+map+=+new+HashMap<String,+String>();
++++map.put("one",+"value");
++++map.put("two",+"value");
++++map.put("three",+"value");
++++System.out.println(map.entrySet());|code-block|syntax|javascript|1521836|对于其他类型的对象，您可以使用reflection为此创建一个utility。|offset|length|1521837|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/developer/technicalArticles/ALT/Reflection/index.html|1|http://www.google.com/search?q=java%2Breflection%2Btostring%2Butility^0|0|0|F|A|0|V|7|1|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@$I|X|J|Y|1|Z]|$I|10|J|11|1|12]]|A|$]]|$1|K|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]|S|$5|N|O|P|A|$Q|T]]]]

Depending on exactly what you want to do, the solution could be fairly simple. The following won't produce the formatted output that print_r provides, but it will allow you to output the structure of lists, arrays, and maps:

<pre><code> // Output a list
 final List&lt;String&gt; list = new ArrayList&lt;String&gt;();
 list.add("one");
 list.add("two");
 list.add("three");
 list.add("four");
 System.out.println(list);

 // Output an array
 final String[] array = {"four", "three", "two", "one"};
 System.out.println(Arrays.asList(array));

 // Output a map
 final Map&lt;String, String&gt; map = new HashMap&lt;String, String&gt;();
 map.put("one", "value");
 map.put("two", "value");
 map.put("three", "value");
 System.out.println(map.entrySet());
</code></pre>

For other types of objects you could use <a href="http://java.sun.com/developer/technicalArticles/ALT/Reflection/index.html" rel="noreferrer" title="Using Java Reflection">reflection</a> to create a <a href="http://www.google.com/search?q=java+reflection+tostring+utility" rel="noreferrer" title="Google Search">utility</a> for this purpose.

blocks|key|1736568|text|您可以尝试一下古老的Apache+Commons+Lang的ToStringBuilder。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1736569|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/lang/api/org/apache/commons/lang/builder/ToStringBuilder.html#reflectionToString(java.lang.Object))^0|U|F|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You might try the good old Apache Commons Lang's <a href="http://commons.apache.org/lang/api/org/apache/commons/lang/builder/ToStringBuilder.html#reflectionToString(java.lang.Object)" rel="noreferrer">ToStringBuilder</a>.

blocks|key|1736728|text|其他人提到了toString()方法。只有当对象实现toString()时，这才真正有用。如果没有正确地实现它，你会得到类似这样的结果：java.lang.Object@1b9240e。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1736729|即使有点单调乏味，在您自己的类中实现toString()仍然很容易，但是第三方类并不总是实现它。您最好使用调试器。像print_r这样的东西在PHP中存在的唯一原因是因为缺乏真正的调试器。我想您会发现，能够设置断点而不是使用一堆诊断打印语句将导致更快的工作流和更干净的代码。|1736730|entityMap^0|6|A|Q|A|1W|O|0|I|A|1M|7|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|I|$]]

Others have mentioned the <code>toString()</code> method. This is really only useful when the object implements <code>toString()</code>. If it has not been implemented properly you will end up with something like this: <code>java.lang.Object@1b9240e</code>.

Even if it is a little tedious it is still easy to implement <code>toString()</code> in your own classes, but third party classes will not always implement it. You are much better off using a debugger. The only reason things like <code>print_r</code> even exist in PHP is because of the lack of a real debugger. I think you will find that being able to set breakpoints instead of using a bunch of diagnostic print statements will result in a much faster workflow and cleaner code.

blocks|key|1736903|text|我对类似print_r的功能的理解是我编写的类RecursiveDump。它并不完美，但它对我来说工作得很好。其用法为：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1736904|String+output+=+RecursiveDump.dump(...);|code-block|syntax|javascript|1736905|它可以使用泛型来改进，这是我多年前写的，在我知道它们之前。此外，虽然它试图处理一些集合类型，但对于对象，它将只调用toString()方法。|1736906|我曾想过使用反射来提取没有适当toString()的类的字段名，但由于Spring+Roo+@RooToString可以为您编写toString()方法...|1736907|当然，另一种选择是使用调试器的检查器工具，但有时使用打印更快。|1736908|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/stivlo/obliquid-lib/blob/master/src/main/java/org/obliquid/helpers/RecursiveDump.java|1|http://www.springsource.org/spring-roo|2|http://static.springsource.org/spring-roo/org.springframework.roo.annotations/apidocs/org/springframework/roo/addon/tostring/RooToString.html^0|4|7|N|D|0|0|0|1L|A|0|F|A|1S|A|Z|A|1|1A|C|2|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@$9|15|A|16|1|17]]|E|$]]|$1|F|3|G|5|H|7|18|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@$9|1H|A|1I|1|1J]|$9|1K|A|1L|1|1M]]|E|$]]|$1|O|3|P|5|6|7|1N|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|1O|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]|Y|$5|T|U|V|E|$W|Z]]|10|$5|T|U|V|E|$W|11]]]]

My take for a Java <code>print_r</code> like functionality, is the class <a href="https://github.com/stivlo/obliquid-lib/blob/master/src/main/java/org/obliquid/helpers/RecursiveDump.java" rel="nofollow">RecursiveDump</a> that I wrote.
It's not perfect, but it is working well for me. The usage is:

<pre><code>String output = RecursiveDump.dump(...);
</code></pre>

It could be improved using generics, I wrote it many years ago, before I knew about them. Also while it tries to deal with some Collection types, with Objects it will just call the <code>toString()</code> method. 

I thought to use Reflection to extract field names for classes without a proper <code>toString()</code>, but since <a href="http://www.springsource.org/spring-roo" rel="nofollow">Spring Roo</a> <a href="http://static.springsource.org/spring-roo/org.springframework.roo.annotations/apidocs/org/springframework/roo/addon/tostring/RooToString.html" rel="nofollow">@RooToString</a> can write the <code>toString()</code> method for you...

Of course the alternative is to use the inspector tool of a debugger, but sometimes is quicker to use prints.

blocks|key|1521482|text|我不知道java中有没有等同于print_r的东西。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1521483|但是..。|1521484|每个对象都有一个toString()方法的默认实现，如果您为它们调用toString()，list和map实现将打印它们的内容。|1521485|如果您需要打印任何调试信息，toString()可能就是您要找的地方。|1521486|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

I don't know of an equivalent of print_r in java.

But...

Every object has a default implementation of the toString() method, the list and map implementations print their contents if you call toString() for them.

If you need any debug information printed out, toString() may be the place you are looking for.

blocks|key|1521650|text|在Java语言中没有print_r的等价物。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1521651|但对于映射或列表，您可以像这样使用foreach-loop：|1521652|List+<String>+list+=+…;+//+fills+your+list+

//+print+each+list+element+

for+(String+s+:+list)+{

+++System.out.println(s);

+}|code-block|syntax|javascript|1521653|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

There is no equivalent for print_r in Java. 

But for maps or lists you can use the foreach-loop like this:

<pre><code>List &lt;String&gt; list = …; // fills your list 

// print each list element 

for (String s : list) {

 System.out.println(s);

 }
</code></pre>

blocks|key|1736673|text|对于数组，最简单的方法是Arrays.asList(数组).toString()。我通常在调试输出中的对象上实现toString()。生成的对象(JAXB等)尽管可能需要创建一个实用程序类来打印它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1736674|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

For arrays the easiest way is Arrays.asList(array).toString() .
I generally implement toString() on objects I like to habe in debug outputs. For generated objects (JAXB etc.) though might need to make an utility class to print it.

last time I asked how to populate a data structure <a href="https://stackoverflow.com/questions/144474/java-arrays-vectors">here</a>. Now I would like to know if there's something in Java, like the <a href="http://www.php.net/print_r" rel="nofollow noreferrer">print_r</a> I use in PHP, to represent what I have populated in the Maps and lists without having to do my own algorithm.

Any ideas?

Java: print_r?

数据结构

调试器

PHP语言

Java

上一次我问到如何填充数据结构。现在，我想知道在Java语言中是否有什么东西，比如我在PHP语言中使用的，来表示我在Map和lists中填充的内容，而不必执行我自己的算法。有什么想法吗？

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