blocks|key|378546|text|列表中的对象必须实现toString才能将有意义的内容打印到屏幕上。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|378547|下面是一个快速测试，看看它们之间的区别：|378548|public+class+Test+{

++++public+class+T1+{
++++++++public+Integer+x;
++++}

++++public+class+T2+{
++++++++public+Integer+x;

++++++++@Override
++++++++public+String+toString()+{
++++++++++++return+x.toString();
++++++++}
++++}

++++public+void+run()+{
++++++++T1+t1+=+new+T1();
++++++++t1.x+=+5;
++++++++System.out.println(t1);

++++++++T2+t2+=+new+T2();
++++++++t2.x+=+5;
++++++++System.out.println(t2);

++++}

++++public+static+void+main(String[]+args)+{++++++++
++++++++new+Test().run();
++++}
}|code-block|syntax|javascript|378549|当这段代码执行时，打印到屏幕的结果是：|378550|t1+=+Test$T1@19821f
t2+=+5|378551|因为T1没有覆盖toString方法，所以它的实例t1打印出来的东西不是很有用。另一方面，T2覆盖了toString，所以我们控制它在I/O中使用时打印的内容，并且我们在屏幕上看到一些更好的东西。|378552|entityMap^0|A|8|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|11|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|T|$]]

The objects in the list must have <code>toString</code> implemented for them to print something meaningful to screen.

Here's a quick test to see the differences:

<pre><code>public class Test {

 public class T1 {
 public Integer x;
 }

 public class T2 {
 public Integer x;

 @Override
 public String toString() {
 return x.toString();
 }
 }

 public void run() {
 T1 t1 = new T1();
 t1.x = 5;
 System.out.println(t1);

 T2 t2 = new T2();
 t2.x = 5;
 System.out.println(t2);

 }

 public static void main(String[] args) { 
 new Test().run();
 }
}
</code></pre>

And when this executes, the results printed to screen are:

<pre><code>t1 = Test$T1@19821f
t2 = 5
</code></pre>

Since T1 does not override the toString method, its instance t1 prints out as something that isn't very useful. On the other hand, T2 overrides toString, so we control what it prints when it is used in I/O, and we see something a little better on screen.

blocks|key|594628|text|下面是一些关于打印list组件的示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|594629|public+class+ListExample+{

++++public+static+void+main(String[]+args)+{
++++++++List<Model>+models+=+new+ArrayList<>();

++++++++//+TODO:+First+create+your+model+and+add+to+models+ArrayList,+to+prevent+NullPointerException+for+trying+this+example

++++++++//+Print+the+name+from+the+list....
++++++++for(Model+model+:+models)+{
++++++++++++System.out.println(model.getName());
++++++++}

++++++++//+Or+like+this...
++++++++for(int+i+=+0;+i+<+models.size();+i%2B%2B)+{
++++++++++++System.out.println(models.get(i).getName());
++++++++}
++++}
}

class+Model+{

++++private+String+name;

++++public+String+getName()+{
++++++++return+name;
++++}

++++public+void+setName(String+name)+{
++++++++this.name+=+name;
++++}
}|code-block|syntax|javascript|594630|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here is some example about getting print out the list component:

<pre><code>public class ListExample {

 public static void main(String[] args) {
 List&lt;Model&gt; models = new ArrayList&lt;&gt;();

 // TODO: First create your model and add to models ArrayList, to prevent NullPointerException for trying this example

 // Print the name from the list....
 for(Model model : models) {
 System.out.println(model.getName());
 }

 // Or like this...
 for(int i = 0; i &lt; models.size(); i++) {
 System.out.println(models.get(i).getName());
 }
 }
}

class Model {

 private String name;

 public String getName() {
 return name;
 }

 public void setName(String name) {
 this.name = name;
 }
}
</code></pre>

blocks|key|378684|text|以下代码紧凑，避免了示例代码中的循环(并给出了很好的逗号)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|378685|System.out.println(Arrays.toString(list.toArray()));|code-block|syntax|javascript|378686|然而，正如其他人所指出的，如果没有为列表中的对象实现合理的toString()方法，那么您将获得正在观察的对象指针(实际上是散列代码)。无论它们是否在列表中，这都是正确的。|378687|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

The following is compact and avoids the loop in your example code (and gives you nice commas):

<pre><code>System.out.println(Arrays.toString(list.toArray()));
</code></pre>

However, as others have pointed out, if you don't have sensible toString() methods implemented for the objects inside the list, you will get the object pointers (hash codes, in fact) you're observing. This is true whether they're in a list or not.

blocks|key|594768|text|从Java8开始，List继承了一个默认的"forEach“方法，您可以将该方法与方法引用"System.out::println”结合使用，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|594769|list.forEach(System.out::println);|code-block|syntax|javascript|594770|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Since Java 8, List inherits a default "forEach" method which you can combine with the method reference "System.out::println" like this:

<pre><code>list.forEach(System.out::println);
</code></pre>

blocks|key|378792|text|System.out.println(list);为我工作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|378793|下面是一个完整的示例：|378794|import+java.util.List;++++
import+java.util.ArrayList;

public+class+HelloWorld+{
+++++public+static+void+main(String[]+args)+{
++++++++final+List<String>+list+=+new+ArrayList<>();
++++++++list.add("Hello");
++++++++list.add("World");
++++++++System.out.println(list);
+++++}
}|code-block|syntax|javascript|378795|它将打印[Hello,+World]。|378796|entityMap^0|0|P|0|0|0|4|E|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|V|8|@$9|W|A|X|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

<code>System.out.println(list);</code> works for me.

Here is a full example:

<pre><code>import java.util.List; 
import java.util.ArrayList;

public class HelloWorld {
 public static void main(String[] args) {
 final List&lt;String&gt; list = new ArrayList&lt;&gt;();
 list.add("Hello");
 list.add("World");
 System.out.println(list);
 }
}
</code></pre>

It will print <code>[Hello, World]</code>.

blocks|key|594834|text|Java+8+Streams方法...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|594835|list.stream().forEach(System.out::println);|code-block|syntax|javascript|594836|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

The Java 8 Streams approach...

<pre><code>list.stream().forEach(System.out::println);
</code></pre>

blocks|key|378843|text|++++list.stream().map(x+->+x.getName()).forEach(System.out::println);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|378844|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code> list.stream().map(x -&gt; x.getName()).forEach(System.out::println);
</code></pre>

blocks|key|378875|text|获取字符串数组列表|type|unstyled|depth|inlineStyleRanges|entityRanges|data|378876|list.forEach(s+->+System.out.println(Arrays.toString((String[])+s+)));|code-block|syntax|javascript|378877|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For a list of array of String

<pre><code>list.forEach(s -&gt; System.out.println(Arrays.toString((String[]) s )));
</code></pre>

blocks|key|378881|text|+++List<String>+textList=++messageList.stream()
++++++++++++++++++++++++++++.map(Message::getText)
++++++++++++++++++++++++++++.collect(Collectors.toList());

++++++++textList.stream().forEach(System.out::println);
++++++++public+class+Message++{

++++++++String+name;
++++++++String+text;

++++++++public+Message(String+name,+String+text)+{
++++++++++++this.name+=+name;
++++++++++++this.text+=+text;
++++++++}

++++++++public+String+getName()+{
++++++++++++return+name;
++++++++}

++++++public+String+getText()+{
++++++++return+text;
+++++}
+++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|378882|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code> List&lt;String&gt; textList= messageList.stream()
 .map(Message::getText)
 .collect(Collectors.toList());

 textList.stream().forEach(System.out::println);
 public class Message {

 String name;
 String text;

 public Message(String name, String text) {
 this.name = name;
 this.text = text;
 }

 public String getName() {
 return name;
 }

 public String getText() {
 return text;
 }
 }
</code></pre>

blocks|key|378893|text|public+static+void+main(String[]+args)+{
++++++++answer(10,60);

++++}
++++public+static+void+answer(int+m,int+k){
++++++++AtomicInteger+n+=+new+AtomicInteger(m);
++++++++Stream<Integer>+stream+=+Stream.generate(()+->+n.incrementAndGet()).limit(k);
++++++++System.out.println(Arrays.toString(stream.toArray()));
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|378894|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>public static void main(String[] args) {
 answer(10,60);

 }
 public static void answer(int m,int k){
 AtomicInteger n = new AtomicInteger(m);
 Stream&lt;Integer&gt; stream = Stream.generate(() -&gt; n.incrementAndGet()).limit(k);
 System.out.println(Arrays.toString(stream.toArray()));
 }
</code></pre>

blocks|key|378938|text|尝试根据需要重写toString()方法，以便打印元素。因此，打印的方法可以是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|378939|for(int+i=0;i<list.size();i%2B%2B){
++++System.out.println(list.get(i).toString());
}+|code-block|syntax|javascript|378940|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

try to override toString() method as you want that the element will be printend. 
so the method to print can be this:

<pre><code>for(int i=0;i&lt;list.size();i++){
 System.out.println(list.get(i).toString());
} 
</code></pre>

blocks|key|378992|text|或者，您可以简单地使用Apache+Commons实用程序：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|378993|https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/ArrayUtils.html#toString-java.lang.Object-|offset|length|378994|List<MyObject>+myObjects+=+...
System.out.println(ArrayUtils.toString(myObjects));|code-block|syntax|javascript|378995|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|3E|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@$D|T|E|U|1|V]]|A|$]]|$1|F|3|G|5|H|7|W|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|C]]]]

Or you could simply use the Apache Commons utilities:

<a href="https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/ArrayUtils.html#toString-java.lang.Object-" rel="noreferrer">https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/ArrayUtils.html#toString-java.lang.Object-</a>

<pre><code>List&lt;MyObject&gt; myObjects = ...
System.out.println(ArrayUtils.toString(myObjects));
</code></pre>

blocks|key|595042|text|我现在碰巧在做这件事...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|595043|List<Integer>+a+=+Arrays.asList(1,+2,+3);
List<Integer>+b+=+Arrays.asList(3,+4);
List<int[]>+pairs+=+a.stream()
++.flatMap(x+->+b.stream().map(y+->+new+int[]{x,+y}))
++.collect(Collectors.toList());

Consumer<int[]>+pretty+=+xs+->+System.out.printf("\n(%25d,%25d)",+xs[0],+xs[1]);
pairs.forEach(pretty);|code-block|syntax|javascript|595044|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I happen to be working on this now...

<pre><code>List&lt;Integer&gt; a = Arrays.asList(1, 2, 3);
List&lt;Integer&gt; b = Arrays.asList(3, 4);
List&lt;int[]&gt; pairs = a.stream()
 .flatMap(x -&gt; b.stream().map(y -&gt; new int[]{x, y}))
 .collect(Collectors.toList());

Consumer&lt;int[]&gt; pretty = xs -&gt; System.out.printf("\n(%d,%d)", xs[0], xs[1]);
pairs.forEach(pretty);
</code></pre>

blocks|key|379058|text|用于打印列表内容的For循环：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|379059|List<String>+myList+=+new+ArrayList<String>();
myList.add("AA");
myList.add("BB");

for+(+String+elem+:+myList+)+{
++System.out.println("Element+:+"%2Belem);
}|code-block|syntax|javascript|379060|结果：|379061|Element+:+AA
Element+:+BB|379062|如果您想要在一行中打印(仅供参考)：|379063|String+strList+=+String.join(",+",+myList);
System.out.println("Elements+:+"%2BstrList);|379064|379065|Elements+:+AA,+BB|379066|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|U|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|V|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|X|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|O|3|H|5|6|7|Z|8|@]|9|@]|A|$]]|$1|P|3|Q|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|R|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|S|$]]

For loop to print the content of a list : 

<pre><code>List&lt;String&gt; myList = new ArrayList&lt;String&gt;();
myList.add("AA");
myList.add("BB");

for ( String elem : myList ) {
 System.out.println("Element : "+elem);
}
</code></pre>

Result : 

<pre><code>Element : AA
Element : BB
</code></pre>

If you want to print in a single line (just for information) : 

<pre><code>String strList = String.join(", ", myList);
System.out.println("Elements : "+strList);
</code></pre>

Result : 

<pre><code>Elements : AA, BB
</code></pre>

blocks|key|379148|text|这取决于List中存储的对象的类型，以及它是否具有toString()方法的实现。System.out.println(list)应该打印所有标准的java对象类型(String、Long、Integer等)。在这种情况下，如果我们使用自定义对象类型，那么我们需要对自定义对象的toString()方法进行override。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|379149|示例：|379150|class+Employee+{
+private+String+name;
+private+long+id;

+@Override
+public+String+toString()+{
+++return+"name:+"+%2B+this.name()+%2B+
+++++++++++",+id:+"+%2B+this.id();
+}++
}|code-block|syntax|javascript|379151|测试：|379152|class+TestPrintList+{
+++public+static+void+main(String[]+args)+{
+++++Employee+employee1+=new+Employee("test1",+123);
+++++Employee+employee2+=new+Employee("test2",+453);
+++++List<Employee>+employees+=+new+ArrayList(2);
+++++employee.add(employee1);
+++++employee.add(employee2);
+++++System.out.println(employees);
+++}
}|379153|entityMap^0|4|4|P|A|15|O|2B|6|2I|4|2N|7|3V|A|49|8|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|19|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1B|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|R|$]]

It depends on what type of objects stored in the <code>List</code>, and whether it has implementation for <code>toString()</code> method. <code>System.out.println(list)</code> should print all the standard java object types (<code>String</code>, <code>Long</code>, <code>Integer</code> etc). In case, if we are using custom object types, then we need to <code>override</code> <code>toString()</code> method of our custom object.

Example:

<pre><code>class Employee {
 private String name;
 private long id;

 @Override
 public String toString() {
 return "name: " + this.name() + 
 ", id: " + this.id();
 } 
}
</code></pre>

Test:

<pre><code>class TestPrintList {
 public static void main(String[] args) {
 Employee employee1 =new Employee("test1", 123);
 Employee employee2 =new Employee("test2", 453);
 List&lt;Employee&gt; employees = new ArrayList(2);
 employee.add(employee1);
 employee.add(employee2);
 System.out.println(employees);
 }
}
</code></pre>

blocks|key|595209|text|例如，使用String.join()：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|595210|System.out.print(String.join("\n",+list));|code-block|syntax|javascript|595211|entityMap^0|5|D|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Use <code>String.join()</code>
for example:
<pre><code>System.out.print(String.join(&quot;\n&quot;, list));
</code></pre>

blocks|key|379255|text|java+11问题的解决方案是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|379256|String+separator+=+",+";
String+toPrint+=+list.stream().map(o+->+String.valueOf(o)).collect(Collectors.joining(separator));

System.out.println(toPrint);|code-block|syntax|javascript|379257|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Solusion of your problem for java 11 is:
<pre class="lang-java prettyprint-override"><code>String separator = &quot;, &quot;;
String toPrint = list.stream().map(o -&gt; String.valueOf(o)).collect(Collectors.joining(separator));

System.out.println(toPrint);
</code></pre>

I am trying to print out all the elements of a <code>List</code>, however it is printing the pointer of the <code>Object</code> rather than the value.

This is my printing code...

<pre><code>for(int i=0;i&lt;list.size();i++){
 System.out.println(list.get(i));
} 
</code></pre>

Could anyone please help me why it isn't printing the value of the elements.

How to print out all the elements of a List in Java?

Java

我试图打印出List的所有元素，但是它打印的是Object的指针，而不是值。这是我的打印代码。for(int i=0;i<list.size();i++){ System.out.println(list.get(i));} 谁能告诉我为什么它不打印元素的值。

问如何在Java中打印出一个列表的所有元素？
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问如何在Java中打印出一个列表的所有元素？
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