blocks|key|1139749|text|Class.forName()为您提供了类对象，这对于反射很有用。这个对象拥有的方法是由Java定义的，而不是由编写类的程序员定义的。它们对于每个类都是相同的。在上面调用newInstance()会给出一个该类的实例(即调用Class.forName("ExampleClass").newInstance()相当于调用new+ExampleClass())，在这个实例上你可以调用类定义的方法，访问可见字段等。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1139750|entityMap^0|34|17|4G|I|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

Class.forName() gives you the class object, which is useful for reflection. The methods that this object has are defined by Java, not by the programmer writing the class. They are the same for every class. Calling newInstance() on that gives you an instance of that class (i.e. calling <code>Class.forName("ExampleClass").newInstance()</code> it is equivalent to calling <code>new ExampleClass()</code>), on which you can call the methods that the class defines, access the visible fields etc.

blocks|key|1355107|text|1:如果你只对类的静态块感兴趣，那么加载类就可以了，并且会执行静态块，那么你所需要的就是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1355108|Class.forName("Somthing");|code-block|syntax|javascript|1355109|2:如果你有兴趣装入类，执行它的静态块，还想访问它的非静态部分，那么你需要一个实例，然后你需要：|1355110|Class.forName("Somthing").newInstance();|1355111|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

1 : if you are interested only in the static block of the class , the loading the class only would do , and would execute static blocks then all you need is:

<pre><code>Class.forName("Somthing");
</code></pre>

2 : if you are interested in loading the class , execute its static blocks and also want to access its its non static part , then you need an instance and then you need:

<pre><code>Class.forName("Somthing").newInstance();
</code></pre>

blocks|key|1139849|text|Class.forName()获取对类的引用时，Class.forName().newInstance()尝试使用类的无参数构造函数来返回新实例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1139850|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|$]]

Class.forName() gets a reference to a Class, Class.forName().newInstance() tries to use the no-arg constructor for the Class to return a new instance.

blocks|key|1354940|text|"Class.forName()“返回给定名称的类类型。"newInstance()“返回这个类的一个实例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1354941|在类型上，你不能直接调用任何实例方法，只能对类使用反射。如果你想使用一个类的对象，你必须创建它的一个实例(与调用“新的MyClass()”相同)。|1354942|"Class.forName()“的示例|1354943|Class+myClass+=+Class.forName("test.MyClass");
System.out.println("Number+of+public+methods:+"+%2B+myClass.getMethods().length);|code-block|syntax|javascript|1354944|"Class.forName().newInstance()“的示例|1354945|MyClass+myClass+=+(MyClass)+Class.forName("test.MyClass").newInstance();
System.out.println("String+representation+of+MyClass+instance:+"+%2B+myClass.toString());|1354946|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|S|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|T|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|V|8|@]|9|@]|A|$I|J]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

"Class.forName()" returns the Class-Type for the given name. "newInstance()" does return an instance of this class.

On the type you can't call directly any instance methods but can only use reflection for the class. If you want to work with an object of the class you have to create an instance of it (same as calling "new MyClass()").

Example for "Class.forName()"

<pre><code>Class myClass = Class.forName("test.MyClass");
System.out.println("Number of public methods: " + myClass.getMethods().length);
</code></pre>

Example for "Class.forName().newInstance()"

<pre><code>MyClass myClass = (MyClass) Class.forName("test.MyClass").newInstance();
System.out.println("String representation of MyClass instance: " + myClass.toString());
</code></pre>

blocks|key|1139914|text|除了上面的回答，当我们有一个需要存在于内存中的静态代码(即代码块是独立于实例的)时，我们可以让类返回，这样我们就可以使用Class.forname("someName")，否则如果我们没有静态代码，我们可以使用Class.forname().newInstance("someName")，因为它会将对象级代码块(非静态)加载到内存中|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1139915|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|$]]

just adding to above answers, when we have a static code (ie code block is instance independent) that needs to be present in memory, we can have the class returned so we'll use Class.forname("someName") else if we dont have static code we can go for Class.forname().newInstance("someName") as it will load object level code blocks(non static) to memory

blocks|key|1140162|text|无论您调用Class.forName()方法多少次，只执行一次静态块而不是多次：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1140163|package+forNameMethodDemo;

public+class+MainClass+{

++++public+static+void+main(String[]+args)+throws+Exception+{
++++++++Class.forName("forNameMethodDemo.DemoClass");
++++++++Class.forName("forNameMethodDemo.DemoClass");
++++++++Class.forName("forNameMethodDemo.DemoClass");
++++++++DemoClass+demoClass+=+(DemoClass)Class.forName("forNameMethodDemo.DemoClass").newInstance();
++++}
}


public+class+DemoClass+{
++++
++++static+{
++++++++System.out.println("in+Static+block");
++++}

++++{
++++++++System.out.println("in+Instance+block");
++++}
}|code-block|syntax|javascript|1140164|输出将为：|1140165|in+Static+block
in+Instance+block|1140166|此in+Static+block语句只打印一次，而不是三次。|offset|length|style|CODE|1140167|entityMap^0|0|0|0|0|1|F|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

No matter how many times you call Class.forName() method, Only once the static block gets executed not multiple time:
<pre class="lang-java prettyprint-override"><code>package forNameMethodDemo;

public class MainClass {

 public static void main(String[] args) throws Exception {
 Class.forName(&quot;forNameMethodDemo.DemoClass&quot;);
 Class.forName(&quot;forNameMethodDemo.DemoClass&quot;);
 Class.forName(&quot;forNameMethodDemo.DemoClass&quot;);
 DemoClass demoClass = (DemoClass)Class.forName(&quot;forNameMethodDemo.DemoClass&quot;).newInstance();
 }
}


public class DemoClass {
 
 static {
 System.out.println(&quot;in Static block&quot;);
 }

 {
 System.out.println(&quot;in Instance block&quot;);
 }
}
</code></pre>
output will be:
<pre><code>in Static block
in Instance block
</code></pre>
This <code>in Static block</code> statement is printed only once not three times.

blocks|key|1140072|text|Class.forName()-->forName()是类类的静态方法，它返回用于反射的类类对象，而不是用户类对象，所以你只能在它上面调用类类方法，如getMethods()，getConstructors()等。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1140073|如果您只关心运行(给定的运行时)类的静态块，并且只获取类的方法、构造函数、修饰符等信息，那么您可以使用Class.forName()来处理此对象|1140074|但是如果你想访问或调用你的类方法(你在运行时给出的类)，那么你需要有它的对象，所以类的newInstance方法为you.It做这件事，创建类的新实例并将它返回给你，.You只需要将它类型转换为你的类。|1140075|ex-：假设Employee是你的班级|1140076|Class+a=Class.forName(args[0]);+

//args[0]=cmd+line+argument+to+give+class+at++runtime.+

Employee+ob1=a.newInstance();|code-block|syntax|javascript|1140077|a.newInstance()类似于使用new+Employee()创建对象。|1140078|现在，您可以访问所有的类可见字段和方法。|1140079|entityMap^0|0|F|23|C|2G|H|0|1F|F|0|0|0|0|0|F|K|E|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|16|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|17|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|18|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|S|3|T|5|6|7|1E|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]]|V|$]]

<code>Class.forName()</code>--&gt;forName() is the static method of Class class it returns Class class object used for reflection not user class object so you can only call Class class methods on it like <code>getMethods()</code>, <code>getConstructors()</code> etc.
If you care about only running static block of your(Runtime given) class and only getting information of methods,constructors,Modifier etc of your class you can do with this object which you get using <code>Class.forName()</code>
But if you want to access or call your class method (class which you have given at runtime) then you need to have its object so newInstance method of Class class do it for you.It create new instance of the class and return it to you .You just need to type-cast it to your class.
ex-: suppose Employee is your class then
<pre class="lang-java prettyprint-override"><code>Class a=Class.forName(args[0]); 

//args[0]=cmd line argument to give class at runtime. 

Employee ob1=a.newInstance();
</code></pre>
<code>a.newInstance()</code> is similar to creating object using <code>new Employee()</code>.
now you can access all your class visible fields and methods.

What is the difference between <code>Class.forName()</code> and <code>Class.forName().newInstance()</code>?

I do not understand the significant difference (I have read something about them!). Could you please help me?

What is the difference between "Class.forName()" and "Class.forName().newInstance()"?

Java

Class.forName()和Class.forName().newInstance()之间的区别是什么我不明白有什么显著的区别(我读过一些关于它们的文章！)。你能帮帮我吗？

问"Class.forName()“和"Class.forName().newInstance()”有什么区别？
EN

回答 7

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问"Class.forName()“和"Class.forName().newInstance()”有什么区别？EN

回答 7

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问"Class.forName()“和"Class.forName().newInstance()”有什么区别？
EN