blocks|key|790427|text|此运算符允许您确定对象的类型。它返回一个boolean值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|790428|例如|790429|package+test;

import+java.util.Date;
import+java.util.Map;
import+java.util.HashMap;

public+class+instanceoftest
{
++++public+static+void+main(String+args[])
++++{
++++++++Map+m=new+HashMap();
++++++++System.out.println("Returns+a+boolean+value+"%2B(m+instanceof+Map));
++++++++System.out.println("Returns+a+boolean+value+"%2B(m+instanceof+HashMap));
++++++++System.out.println("Returns+a+boolean+value+"%2B(m+instanceof+Object));
++++++++System.out.println("Returns+a+boolean+value+"%2B(m+instanceof+Date));
++++}
}+|code-block|syntax|javascript|790430|输出为：|790431|Returns+a+boolean+value+true
Returns+a+boolean+value+true
Returns+a+boolean+value+true
Returns+a+boolean+value+false|790432|entityMap^0|K|7|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|X|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|R|$]]

This operator allows you to determine the type of an object.
It returns a <code>boolean</code> value.

For example

<pre><code>package test;

import java.util.Date;
import java.util.Map;
import java.util.HashMap;

public class instanceoftest
{
 public static void main(String args[])
 {
 Map m=new HashMap();
 System.out.println("Returns a boolean value "+(m instanceof Map));
 System.out.println("Returns a boolean value "+(m instanceof HashMap));
 System.out.println("Returns a boolean value "+(m instanceof Object));
 System.out.println("Returns a boolean value "+(m instanceof Date));
 }
} 
</code></pre>

the output is:

<pre><code>Returns a boolean value true
Returns a boolean value true
Returns a boolean value true
Returns a boolean value false
</code></pre>

blocks|key|574052|text|如果source是一个object变量，那么instanceof就是一种检查它是否是Button的方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|574053|entityMap^0|2|6|B|6|M|A|16|6|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|G|$]]

If <code>source</code> is an <code>object</code> variable, <code>instanceof</code> is a way of checking to see if it is a <code>Button</code> or not.

blocks|key|790439|text|public+class+Animal{+float+age;+}

public+class+Lion+extends+Animal+{+int+claws;}

public+class+Jungle+{
++++public+static+void+main(String+args[])+{

++++++++Animal+animal+=+new+Animal();+
++++++++Animal+animal2+=+new+Lion();+
++++++++Lion+lion+=+new+Lion();+
++++++++Animal+animal3+=+new+Animal();+
++++++++Lion+lion2+=+new+Animal();+++//won't+compile+(can't+reference+super+class+object+with+sub+class+reference+variable)+

++++++++if(animal+instanceof+Lion)++//false

++++++++if(animal2+instanceof+Lion)++//true

++++++++if(lion+insanceof+Lion)+//true

++++++++if(animal3+instanceof+Animal)+//true+

++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|790440|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 class Animal{ float age; }

public class Lion extends Animal { int claws;}

public class Jungle {
 public static void main(String args[]) {

 Animal animal = new Animal(); 
 Animal animal2 = new Lion(); 
 Lion lion = new Lion(); 
 Animal animal3 = new Animal(); 
 Lion lion2 = new Animal(); //won't compile (can't reference super class object with sub class reference variable) 

 if(animal instanceof Lion) //false

 if(animal2 instanceof Lion) //true

 if(lion insanceof Lion) //true

 if(animal3 instanceof Animal) //true 

 }
}
</code></pre>

blocks|key|574409|text|可用作相等检查中的速记。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|574410|所以这段代码|574411|if(ob+!=+null+&&+this.getClass()+==+ob.getClass)+{
}|code-block|syntax|javascript|574412|可以写成|574413|if(ob+instanceOf+ClassA)+{
}|574414|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|$]]

Can be used as a shorthand in equality check.
So this code
<pre><code>if(ob != null &amp;&amp; this.getClass() == ob.getClass) {
}
</code></pre>
can be written as
<pre><code>if(ob instanceOf ClassA) {
}
 
</code></pre>

blocks|key|790510|text|当你想知道特定对象的实例时，关键字的实例是很有帮助的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|790511|假设你抛出了异常，当你有了捕获，然后执行sum自定义操作，然后再次按照你的逻辑继续(抛出或记录等)|790512|示例:+1)用户创建自定义异常"InvalidExtensionsException“，按照逻辑抛出|790513|2)现在在catch块catch+(异常e)+{如果异常类型是"InvalidExtensionsException“，则执行sum逻辑|790514|InvalidExtensionsException+InvalidException+=(InvalidExtensionsException)e;|code-block|syntax|javascript|790515|3)如果你没有检查的实例，并且异常类型是空指针异常，你的代码将会崩溃。|790516|所以你的逻辑应该在if+(e+instanceof+InvalidExtensionsException){+InvalidExtensionsException+InvalidException+=(InvalidExtensionsException)e；}的实例中|790517|上面的例子是错误的编码实践，但是这个例子可以帮助你理解它的实例的用法。|790518|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|X|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|Y|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

Instance of keyword is helpful when you want to know particular object's instance .

Suppose you are throw exception and when you have catch then perform sum custom operation and then again continue as per your logic (throws or log etc)

Example :
1) User created custom exception "InvalidExtensionsException" and throw it as per logic

2) Now in catch block 
catch (Exception e) {
 perform sum logic if exception type is "InvalidExtensionsException"

<pre><code>InvalidExtensionsException InvalidException =(InvalidExtensionsException)e;
</code></pre>

3) If you are not checking instance of and exception type is Null pointer exception your code will break.

So your logic should be inside of instance of 
 if (e instanceof InvalidExtensionsException){ 
 InvalidExtensionsException InvalidException =(InvalidExtensionsException)e;
 } 

Above example is wrong coding practice However this example is help you to understand use of instance of it.

blocks|key|574508|text|在JDK16中，引入了instanceof的模式匹配。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|574509|之前：|574510|if+(obj+instanceof+StringBuilder)+{
++StringBuilder+builder+=+(StringBuilder)+obj;
++builder.append("Hello+StackOverflow")
}|code-block|syntax|javascript|574511|现在：|574512|if+(obj+instanceof+StringBuilder+builder)+{
++builder.append("Hello+StackOverflow")
}|574513|574514|public+boolean+equals(Object+o)+{
++if+(!(o+instanceof+StringBuilder))+{
++++return+false;
++}
++StringBuilder+other+=+(StringBuilder)+o;
++return+//Logic
}|574515|574516|public+boolean+equals(Object+o)+{
++return+(o+instanceof+StringBuilder+other)
++//Logic
}|574517|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|M|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|N|3|O|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|P|3|J|5|6|7|11|8|@]|9|@]|A|$]]|$1|Q|3|R|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|S|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|T|$]]

In JDK 16 pattern matching for instanceof was introduced.
Before:
<pre><code>if (obj instanceof StringBuilder) {
 StringBuilder builder = (StringBuilder) obj;
 builder.append(&quot;Hello StackOverflow&quot;)
}
</code></pre>
Now:
<pre><code>if (obj instanceof StringBuilder builder) {
 builder.append(&quot;Hello StackOverflow&quot;)
}
</code></pre>
Before:
<pre><code>public boolean equals(Object o) {
 if (!(o instanceof StringBuilder)) {
 return false;
 }
 StringBuilder other = (StringBuilder) o;
 return //Logic
}
</code></pre>
Now:
<pre><code>public boolean equals(Object o) {
 return (o instanceof StringBuilder other)
 //Logic
}
</code></pre>

blocks|key|790628|text|class+Test48{
public+static+void+main+(String+args[]){
Object+Obj=new+Hello();
//Hello+obj=new+Hello;
System.out.println(Obj+instanceof+String);
System.out.println(Obj+instanceof+Hello);
System.out.println(Obj+instanceof+Object);
Hello+h=null;
System.out.println(h+instanceof+Hello);
System.out.println(h+instanceof+Object);
}
}++|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|790629|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>class Test48{
public static void main (String args[]){
Object Obj=new Hello();
//Hello obj=new Hello;
System.out.println(Obj instanceof String);
System.out.println(Obj instanceof Hello);
System.out.println(Obj instanceof Object);
Hello h=null;
System.out.println(h instanceof Hello);
System.out.println(h instanceof Object);
}
} 
</code></pre>

blocks|key|574107|text|非常简单的代码示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|574108|If+(object1+instanceof+Class1)+{
+++//+do+something
}+else+if+(object1+instanceof+Class2)+{
+++//+do+something+different
}|code-block|syntax|javascript|574109|这里要当心。在上面的示例中，如果Class1是Object，则第一次比较将始终为真。因此，就像处理异常一样，层次顺序也很重要！|574110|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|$]]

Very simple code example:

<pre><code>If (object1 instanceof Class1) {
 // do something
} else if (object1 instanceof Class2) {
 // do something different
}
</code></pre>

Be careful here. In the example above, if Class1 is Object, the first comparison will always be true. So, just like with exceptions, hierarchical order matters!

blocks|key|790463|text|您可以使用Map对实例进行更高的抽象|type|unstyled|depth|inlineStyleRanges|entityRanges|data|790464|private+final+Map<Class,+Consumer<String>>+actions+=+new+HashMap<>();|code-block|syntax|javascript|790465|然后让这样的map向其添加一些操作：|790466|actions.put(String.class,+new+Consumer<String>()+{
++++++++@Override
++++++++public+void+accept(String+s)+{
+++++++++++System.out.println("action+for+String");+++++++
++++++++}
++++};|790467|然后，拥有一个未知类型的对象，您可以从该映射中获得特定的操作：|790468|actions.get(someObject).accept(someObject)|790469|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]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

You could use Map to make higher abstraction on instance of

<pre><code>private final Map&lt;Class, Consumer&lt;String&gt;&gt; actions = new HashMap&lt;&gt;();
</code></pre>

Then having such map add some action to it:

<pre><code>actions.put(String.class, new Consumer&lt;String&gt;() {
 @Override
 public void accept(String s) {
 System.out.println("action for String"); 
 }
 };
</code></pre>

Then having an Object of not known type you could get specific action from that map:

<pre><code>actions.get(someObject).accept(someObject)
</code></pre>

blocks|key|574455|text|instanceof操作符用于检查对象是否为指定类型的实例。(类或子类或接口)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|574456|instanceof也称为类型比较运算符，因为它将实例与类型进行比较。它返回true或false。|574457|class+Simple1+{++
public+static+void+main(String+args[])+{++
Simple1+s=new+Simple1();++
System.out.println(s+instanceof+Simple1);+//true++
}++
}++|code-block|syntax|javascript|574458|如果我们将instanceof运算符应用于任何具有空值的变量，它将返回false。|574459|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

The instanceof operator is used to check whether the object is an instance of the specified type. (class or subclass or interface).

The instanceof is also known as type comparison operator because it compares the instance with type. It returns either true or false.

<pre><code>class Simple1 { 
public static void main(String args[]) { 
Simple1 s=new Simple1(); 
System.out.println(s instanceof Simple1); //true 
} 
} 
</code></pre>

If we apply the instanceof operator with any variable that has null value, it returns false.

What is the <code>instanceof</code> operator used for? I've seen stuff like

<pre><code>if (source instanceof Button) {
 //...
} else {
 //...
}
</code></pre>

But none of it made sense to me. I've done my research, but came up only with examples without any explanations.

What is the 'instanceof' operator used for in Java?

instanceof操作符是用来做什么的？我见过像这样的东西if (source instanceof Button) {    //...} else {    //...}但这一切对我来说都没什么意义。我已经做了研究，但只提出了一些例子，没有任何解释。

问在Java中'instanceof‘运算符是用来做什么的？
EN

回答 10

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问在Java中'instanceof‘运算符是用来做什么的？EN

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问在Java中'instanceof‘运算符是用来做什么的？
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