blocks|key|2042146|text|可以，您可以使用反射、使用Class.forName(名称)、抓取构造函数并调用它，在给定字符串名称的类路径上加载一个类。我来给你举个例子。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2042147|假设我有一个类：|2042148|com.crossedstreams.thingy.Foo|code-block|syntax|javascript|2042149|它有一个带签名的构造函数：|2042150|Foo(String+a,+String+b);|2042151|我将根据这两个事实实例化这个类，如下所示：|2042152|//+Load+the+Class.+Must+use+fully+qualified+name+here!
Class+clazz+=+Class.forName("com.crossedstreams.thingy.Foo");

//+I+need+an+array+as+follows+to+describe+the+signature
Class[]+parameters+=+new+Class[]+{String.class,+String.class};

//+Now+I+can+get+a+reference+to+the+right+constructor
Constructor+constructor+=+clazz.getConstructor(parameters);

//+And+I+can+use+that+Constructor+to+instantiate+the+class
Object+o+=+constructor.newInstance(new+Object[]+{"one",+"two"});

//+To+prove+it's+really+there...
System.out.println(o);|2042153|输出：|2042154|com.crossedstreams.thingy.Foo@20cf2c80|2042155|有很多资源详细介绍了这一点，你应该意识到你引入了一个编译器无法为你检查的依赖项-如果你拼错了类名或任何东西，它将在运行时失败。此外，在此过程中可能会抛出许多不同类型的异常。不过，这是一种非常强大的技术。|2042156|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|15|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|16|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

Yes, you can load a class on your classpath given the String name using reflection, using Class.forName(name), grabbing the constructor and invoking it. I'll do you an example.

Consider I have a class:

<pre><code>com.crossedstreams.thingy.Foo
</code></pre>

Which has a constructor with signature:

<pre><code>Foo(String a, String b);
</code></pre>

I would instantiate the class based on these two facts as follows:

<pre><code>// Load the Class. Must use fully qualified name here!
Class clazz = Class.forName("com.crossedstreams.thingy.Foo");

// I need an array as follows to describe the signature
Class[] parameters = new Class[] {String.class, String.class};

// Now I can get a reference to the right constructor
Constructor constructor = clazz.getConstructor(parameters);

// And I can use that Constructor to instantiate the class
Object o = constructor.newInstance(new Object[] {"one", "two"});

// To prove it's really there...
System.out.println(o);
</code></pre>

Output:

<pre><code>com.crossedstreams.thingy.Foo@20cf2c80
</code></pre>

There's plenty of resources out there which go into more detail about this, and you should be aware that you're introducing a dependency that the compiler can't check for you - if you misspell the class name or anything, it will fail at runtime.
Also, there's quite a few different types of Exception that might be throws during this process. It's a very powerful technique though.

blocks|key|2042214|text|这就是你想要做的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2042215|String+className+=+"Class1";
Object+xyz+=+Class.forName(className).newInstance();|code-block|syntax|javascript|2042216|请注意，newInstance方法不允许使用参数化构造函数。(请参阅Class.newInstance+documentation|offset|length|2042217|如果你确实需要使用参数化的构造函数，这就是你需要做的：|2042218|import+java.lang.reflect.*;

Param1Type+param1;
Param2Type+param2;
String+className+=+"Class1";
Class+cl+=+Class.forName(className);
Constructor+con+=+cl.getConstructor(Param1Type.class,+Param2Type.class);
Object+xyz+=+con.newInstance(param1,+param2);|2042219|请参阅Constructor.newInstance+documentation|2042220|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/javase/6/docs/api/java/lang/Class.html#newInstance(%2529)|1|http://java.sun.com/javase/6/docs/api/java/lang/reflect/Constructor.html#newInstance(java.lang.Object...)^0|0|0|Y|V|0|0|0|0|3|11|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@$I|13|J|14|1|15]]|A|$]]|$1|K|3|L|5|6|7|16|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|18|8|@]|9|@$I|19|J|1A|1|1B]]|A|$]]|$1|Q|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]|Y|$5|T|U|V|A|$W|Z]]]]

This is what you want to do:

<pre><code>String className = "Class1";
Object xyz = Class.forName(className).newInstance();
</code></pre>

Note that the newInstance method does not allow a parametrized constructor to be used. (See <a href="http://java.sun.com/javase/6/docs/api/java/lang/Class.html#newInstance()" rel="noreferrer">Class.newInstance documentation</a>)

If you do need to use a parametrized constructor, this is what you need to do:

<pre><code>import java.lang.reflect.*;

Param1Type param1;
Param2Type param2;
String className = "Class1";
Class cl = Class.forName(className);
Constructor con = cl.getConstructor(Param1Type.class, Param2Type.class);
Object xyz = con.newInstance(param1, param2);
</code></pre>

See <a href="http://java.sun.com/javase/6/docs/api/java/lang/reflect/Constructor.html#newInstance(java.lang.Object...)" rel="noreferrer">Constructor.newInstance documentation</a>

blocks|key|2042271|text|这应该是可行的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2042272|import+java.lang.reflect.*;

FirstArgType+arg1;
SecondArgType+arg2;
Class+cl+=+Class.forName("TheClassName");
Constructor+con+=+cl.getConstructor(FirstArgType.class,+SecondArgType.class);
Object+obj+=+con.newInstance(arg1,+arg2);|code-block|syntax|javascript|2042273|从那里你可以转换成一个已知类型。|2042274|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|$]]

This should work:

<pre><code>import java.lang.reflect.*;

FirstArgType arg1;
SecondArgType arg2;
Class cl = Class.forName("TheClassName");
Constructor con = cl.getConstructor(FirstArgType.class, SecondArgType.class);
Object obj = con.newInstance(arg1, arg2);
</code></pre>

From there you can cast to a known type.

blocks|key|2042313|text|另一个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2042314|import+java.lang.reflect.Constructor;

public+class+Test+{

+public+Test(String+name)+{
++++this.name+=+name;
+}

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

+public+String+toString()+{
++++return+this.name;
+}

+private+String+name;

+public+static+void+main(String[]+args)+throws+Exception+{
++++String+className+=+"Test";
++++Class+clazz+=+Class.forName(className);
++++Constructor+tc+=+clazz.getConstructor(String.class);
++++Object+t+=+tc.newInstance("John");
++++System.out.println(t);
+}
}|code-block|syntax|javascript|2042315|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|$]]

Another one:

<pre><code>import java.lang.reflect.Constructor;

public class Test {

 public Test(String name) {
 this.name = name;
 }

 public String getName() {
 return name;
 }

 public String toString() {
 return this.name;
 }

 private String name;

 public static void main(String[] args) throws Exception {
 String className = "Test";
 Class clazz = Class.forName(className);
 Constructor tc = clazz.getConstructor(String.class);
 Object t = tc.newInstance("John");
 System.out.println(t);
 }
}
</code></pre>

blocks|key|2042426|text|对于我来说，这在JDK7中工作得更干净一些，而上面的答案让事情比从新手的角度来看更加困难：(假设您已经将'className‘声明为作为方法参数传递的字符串变量，或者在使用以下代码的方法中声明为字符串变量)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2042427|Class<?>+panel+=+Class.forName(+className+);
JPanel+newScreen+=+(JPanel)+panel.newInstance();|code-block|syntax|javascript|2042428|从这一点起，您可以使用动态命名类中的属性/方法，就像您期望能够使用它们一样：|2042429|JFrame+frame+=+new+JFrame();+//+<<<+Just+so+no-one+gets+lost+here
frame.getContentPane().removeAll();
frame.getContentPane().add(+newScreen+);
frame.validate();
frame.repaint();|2042430|当我尝试将新的'+object‘类型的对象.add()到框架中时，上面其他答案中的示例导致了错误。这里展示的技术给了我一个有用的对象，上面只有两行代码。|2042431|不太确定为什么会这样--我自己也是个Java新手。|2042432|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

This worked a little more cleanly for me in JDK7, while the answers above made things a bit more difficult than they needed to be from a newbie perspective: (assumes you've declared 'className' as a String variable passed as a method parameter or earlier in the method using this code):

<pre><code>Class&lt;?&gt; panel = Class.forName( className );
JPanel newScreen = (JPanel) panel.newInstance();
</code></pre>

From this point you can use properties / methods from your dynamically-named class exactly as you would expect to be able to use them:

<pre><code>JFrame frame = new JFrame(); // &lt;&lt;&lt; Just so no-one gets lost here
frame.getContentPane().removeAll();
frame.getContentPane().add( newScreen );
frame.validate();
frame.repaint();
</code></pre>

The examples in other answers above resulted in errors when I tried to .add() the new 'Object' type object to the frame. The technique shown here gave me a usable object with just those 2 lines of code above.

Not exactly certain why that was - I'm a Java newbie myself.

Is there a way to create a new class from a String variable in Java?

<pre><code>String className = "Class1";
//pseudocode follows
Object xyz = new className(param1, param2);
</code></pre>

Also, if possible does the resulting object have to be of type Object?

There may be a better way, but I want to be able to retrieve values from an XML file, then instantiate the classes named after those strings. Each of these classes implement the same interface and are derived from the same parent class, so I would then be able to call a particular method in that class.

Create new object from a string in Java

编译器

Java

在Java中，有没有办法从字符串变量创建一个新类？String className = "Class1";//pseudocode followsObject xyz = new className(param1, param2);另外，如果可能的话，结果对象必须是Object类型吗？也许有一种更好的方法，但我希望能够...

问在Java中从字符串创建新对象
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