blocks|key|1251355|text|Java不支持输出参数。您可以使用返回值，或者将对象作为参数传入并修改该对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1251356|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|$]]

Java does not support output parameters. You can use a return value, or pass in an object as a parameter and modify the object.

blocks|key|1251414|text|作为一种解决办法，可以使用通用的"ObjectHolder“。请参阅下面的代码示例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1251415|示例输出为：|1251416|name:+John+Doe
dob:1953-12-17
name:+Jim+Miller
dob:1947-04-18|code-block|syntax|javascript|1251417|因此Person参数已经被修改，因为它被包装在通过值传递的Holder中-里面的泛型参数是一个可以修改内容的引用-所以实际上返回了一个不同的person，原始的保持原样。|1251418|/**
+*+show+work+around+for+missing+call+by+reference+in+java
+*/
public+class+OutparamTest+{

+/**
++*+a+test+class+to+be+used+as+parameter
++*/
+public+static+class+Person+{
+++public+String+name;
+++++public+String+dob;
+++++public+void+show()+{
++++++System.out.println("name:+"%2Bname%2B"\ndob:"%2Bdob);
+++}
+}

+/**
++*+ObjectHolder+(Generic+ParameterWrapper)
++*/
+public+static+class+ObjectHolder<T>+{
++++public+ObjectHolder(T+param)+{
+++++this.param=param;
++++}
++++public+T+param;
+}

+/**
++*+ObjectHolder+is+substitute+for+missing+"out"+parameter
++*/
+public+static+void+setPersonData(ObjectHolder<Person>+personHolder,String+name,String+dob)+{
++++//+Holder+needs+to+be+dereferenced+to+get+access+to+content
++++personHolder.param=new+Person();
++++personHolder.param.name=name;
++++personHolder.param.dob=dob;
+}+

++/**
+++*+show+how+it+works
+++*/
++public+static+void+main(String+args[])+{
++++Person+jim=new+Person();
++++jim.name="Jim+Miller";
++++jim.dob="1947-04-18";
++++ObjectHolder<Person>+testPersonHolder=new+ObjectHolder(jim);
++++//+modify+the+testPersonHolder+person+content+by+actually+creating+and+returning
++++//+a+new+Person+in+the+"out+parameter"
++++setPersonData(testPersonHolder,"John+Doe","1953-12-17");
++++testPersonHolder.param.show();
++++jim.show();
++}
}|1251419|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

As a workaround a generic "ObjectHolder" can be used. See code example below. 

The sample output is:

<pre><code>name: John Doe
dob:1953-12-17
name: Jim Miller
dob:1947-04-18
</code></pre>

so the Person parameter has been modified since it's wrapped in the Holder which is passed by value - the generic param inside is a reference where the contents can be modified - so actually a different person is returned and the original stays as is.

<pre><code>/**
 * show work around for missing call by reference in java
 */
public class OutparamTest {

 /**
 * a test class to be used as parameter
 */
 public static class Person {
 public String name;
 public String dob;
 public void show() {
 System.out.println("name: "+name+"\ndob:"+dob);
 }
 }

 /**
 * ObjectHolder (Generic ParameterWrapper)
 */
 public static class ObjectHolder&lt;T&gt; {
 public ObjectHolder(T param) {
 this.param=param;
 }
 public T param;
 }

 /**
 * ObjectHolder is substitute for missing "out" parameter
 */
 public static void setPersonData(ObjectHolder&lt;Person&gt; personHolder,String name,String dob) {
 // Holder needs to be dereferenced to get access to content
 personHolder.param=new Person();
 personHolder.param.name=name;
 personHolder.param.dob=dob;
 } 

 /**
 * show how it works
 */
 public static void main(String args[]) {
 Person jim=new Person();
 jim.name="Jim Miller";
 jim.dob="1947-04-18";
 ObjectHolder&lt;Person&gt; testPersonHolder=new ObjectHolder(jim);
 // modify the testPersonHolder person content by actually creating and returning
 // a new Person in the "out parameter"
 setPersonData(testPersonHolder,"John Doe","1953-12-17");
 testPersonHolder.param.show();
 jim.show();
 }
}
</code></pre>

blocks|key|1251430|text|将传递到不同类中的值包装在不同的类中，这可能会对实现此技巧有所帮助，请查看下面的更多真实示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1251431|++class+Ref<T>{

++++T+s;

++++public+void+set(T+value){
++++++++s+=++value;
++++}

++++public+T+get(){
++++++++return+s;
++++}

++++public+Ref(T+value)+{
++++++++s+=+value;
++++}
}


class+Out<T>{

++++T+s;

++++public+void+set(T+value){
++++++++s+=++value;
++++}
++++public+T+get(){
++++++++return+s;
++++}

++++public+Out()+{
++++}
}

public+static+void+doAndChangeRefs+(Ref<String>+str,+Ref<Integer>+i,+Out<String>+str2){
++++//refs+passed+..+set+value
++++str.set("def");
++++i.set(10);

++++//out+param+passed+as+null+..+instantiate+and+set+
++++str2+=+new+Out<String>();
++++str2.set("hello+world");
}
public+static+void+main(String+args[])+{
++++++++Ref<Integer>++iRef+=+new+Ref<Integer>(11);
++++++++Out<String>+strOut+=+null;+
++++++++doAndChangeRefs(new+Ref<String>("test"),+iRef,+strOut);
++++++++System.out.println(iRef.get());
++++++++System.out.println(strOut.get());

++++}|code-block|syntax|javascript|1251432|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|$]]

Wrap the value passed in different classes that might be helpful doing the trick, check below for more real example: 

<pre><code> class Ref&lt;T&gt;{

 T s;

 public void set(T value){
 s = value;
 }

 public T get(){
 return s;
 }

 public Ref(T value) {
 s = value;
 }
}


class Out&lt;T&gt;{

 T s;

 public void set(T value){
 s = value;
 }
 public T get(){
 return s;
 }

 public Out() {
 }
}

public static void doAndChangeRefs (Ref&lt;String&gt; str, Ref&lt;Integer&gt; i, Out&lt;String&gt; str2){
 //refs passed .. set value
 str.set("def");
 i.set(10);

 //out param passed as null .. instantiate and set 
 str2 = new Out&lt;String&gt;();
 str2.set("hello world");
}
public static void main(String args[]) {
 Ref&lt;Integer&gt; iRef = new Ref&lt;Integer&gt;(11);
 Out&lt;String&gt; strOut = null; 
 doAndChangeRefs(new Ref&lt;String&gt;("test"), iRef, strOut);
 System.out.println(iRef.get());
 System.out.println(strOut.get());

 }
</code></pre>

Could someone please give me some sample code that uses an output parameter in function? I've tried to Google it but just found it just in functions. I'd like to use this output value in another function.

The code I am developing intended to be run in Android.

How to use an output parameter in Java?

Android

Java

有人能给我一些在函数中使用输出参数的示例代码吗？我试着用谷歌搜索它，但只是在函数中找到了它。我想在另一个函数中使用这个输出值。我正在开发的代码打算在Android上运行。

问如何在Java中使用输出参数？
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