blocks|key|691073|text|死代码是永远不会执行的代码，例如|type|unstyled|depth|inlineStyleRanges|entityRanges|data|691074|+boolean+b+=+true
+if+(!b)+{
++++....+
++++//+dead+code+here
+}|code-block|syntax|javascript|691075|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|$]]

Dead code is code that will never be executed, e.g.

<pre><code> boolean b = true
 if (!b) {
 .... 
 // dead code here
 }
</code></pre>

blocks|key|691148|text|Eclipse提供了两种类型的诊断，用于标记在运行时将执行/可能不执行的代码。1)不可达代码:这些是通常的java警告，遵循JLS的不可达规则，也由javac给出。这些都是编译错误。示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|691149|+++int+foo()+{
++++++return+1;
++++++int+i+=+1;+//+Unreachable
+++}
+++int+foo2()+{
+++++while+(true);
+++++int+i+=1;+//Unreachable
+++}|code-block|syntax|javascript|691150|还有其他更复杂的示例:)|691151|2)死代码:这是Eclipse自己的静态分析警告，并且主要与空分析绑定在一起。|691152|+++void+foo()+{
+++++Object+o+=+null;
+++++if+(o+==+null)+{
+++++}+else+{
+++++//+dead+code
+++++}|691153|上面给出的例子不应该给出一个死代码警告。即|691154|boolean+x+=+true;
if+(x)+{
+++//+do+something
}+else+{
+++//+this+is+dead+code!
}|691155|不应该给出警告，因为JLS禁止编译器计算变量的“值”。我们能评估的就是'nullness‘|691156|希望这能有所帮助|691157|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

There are two kinds of diagnostics that Eclipse gives out for marking code that will/may not be executed at runtime. 
1) Unreachable code: These are the usual java warnings that follow the unreachability rules of the JLS, and are also given by javac. These are meant to be compile errors. Examples:

<pre><code> int foo() {
 return 1;
 int i = 1; // Unreachable
 }
 int foo2() {
 while (true);
 int i =1; //Unreachable
 }
</code></pre>

There are other more complicated examples :)

2) Dead code: This is Eclipse's own static analysis warnings, and are mostly tied out of the null analysis i.e.

<pre><code> void foo() {
 Object o = null;
 if (o == null) {
 } else {
 // dead code
 }
</code></pre>

The examples given above should NOT give a dead code warning. i.e. 

<pre><code>boolean x = true;
if (x) {
 // do something
} else {
 // this is dead code!
}
</code></pre>

should not give the warning, because JLS forbids the compiler to evaluate the 'value' of variables. All that we can evaluate is the 'nullness'

Hope this helps

blocks|key|691270|text|您可能在"Dead+Code“行上方的行中有一个空指针异常。确保检查"Null+Pointer“异常。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|691271|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|$]]

You might be having an Null pointer exception in the lines above the "Dead Code" lines.
Make sure you check for "Null Pointer" exception.

blocks|key|691430|text|您可能以前使用过变量ar。则编译器知道else语句中的行将永远不会被执行。要么在您使用ar的地方有一个NullPointerException，要么执行if语句的第一部分。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|691431|entityMap^0|A|2|17|2|1F|K|24|2|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|$]]

It is possible that you have used the variable <code>ar</code> before. Then the compiler knows that the line in the else statement will never be executed. Either there will be a <code>NullPointerException</code> at the place where you used <code>ar</code> or the first part of the <code>if</code> statement will be executed.

blocks|key|475351|text|发生这种情况的另一种情况。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|475352|System.out.println("result+:"+%2B+result+%2B+":"+%2B+result.isEmpty());
if+(result+==+null)
++++return+result;
else+if(!result.isEmpty())
++++str.append(result+%2B+"+");|code-block|syntax|javascript|475353|1)在这里，当您打印结果并检查isEmpty()时，eclipse假设结果不是空的，因此它不会进入if。所以返回结果是死码。|475354|2)现在假设结果为null，因此您将在result.isEmpty()中获得NullPointerException，因此，如果返回结果为死码，则它将不再进入|475355|要实现这一点，只需注释掉System.out.println()。|475356|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Some other case when this happens.

<pre><code>System.out.println("result :" + result + ":" + result.isEmpty());
if (result == null)
 return result;
else if(!result.isEmpty())
 str.append(result + " ");
</code></pre>

1) Here as you you are printing result and checking isEmpty() eclipse assumes that result is not null so it will not go in if. So return result is dead code.

2)Now let say result is coming null so you will get NullPointerException in result.isEmpty() so again it will not go in if and return result is deadcode

To make this work just comment out System.out.println().

blocks|key|691584|text|如果您提供的条件检查可能永远不会得到满足，Eclipse将发出此警告。以下是一些示例|type|unstyled|depth|inlineStyleRanges|entityRanges|data|691585|Object+o=null;
if(o!=null)+{
+//Some+code

}|code-block|syntax|javascript|691586|此处将出现死代码警告，因为对象已设置为空|691587|下面给出了另一个例子|691588|BSTTest+bstTest=null;
bstTest.test=10;
if(bstTest==null)+{
++//some+code

}|691589|这里的代码试图访问类的一个变量。由于变量已经被访问，eclipse将在if(bstTest==null)中给出死代码警告，因为当变量已经被访问时，bstTest可能不为null。|691590|注意:这里bstTest.test会给出空指针异常|691591|entityMap^0|0|0|0|0|0|0|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]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Eclipse gives this warning if the condition check you are giving may never be satisfied. Following are some examples

<pre><code>Object o=null;
if(o!=null) {
 //Some code

}
</code></pre>

Here Dead code warning will come as Object is already made null

Another example is given below

<pre><code>BSTTest bstTest=null;
bstTest.test=10;
if(bstTest==null) {
 //some code

}
</code></pre>

Here the code is trying to access a variable of the class. As the variable is already accessed, eclipse will give dead code warning in if(bstTest==null) as bstTest may not be null when the variable is already accessed.

Note: Here bstTest.test will give null pointer exception

blocks|key|475484|text|死代码是我们的代码中永远不会执行运行时的部分，它的无用的示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|475485|if(false){+//+statements+}|code-block|syntax|javascript|475486|有关更多示例，请参阅：DeadCode+Examples|offset|length|475487|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dynamicsax-2012/developer/dead-code-examples^0|0|0|B|H|0|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]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

Dead code is the section of our code that is never going to execute runtime, its useless
EX:

<pre><code>if(false){ // statements }
</code></pre>

For more example u can refer : <a href="https://docs.microsoft.com/en-us/dynamicsax-2012/developer/dead-code-examples" rel="nofollow noreferrer">DeadCode Examples</a>

blocks|key|475179|text|试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|475180|while+(true)+{
++++if(false+==+true)+break;

}

S.O.P("I+will+never+reach+here!")+<--+This+code+will+never+be+executed.|code-block|syntax|javascript|475181|代码是有效的，因为它符合编译器，但是在现实中，循环永远不会退出，实际上S.O.P永远不会执行。|475182|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|$]]

Try this:

<pre><code>while (true) {
 if(false == true) break;

}

S.O.P("I will never reach here!") &lt;-- This code will never be executed.
</code></pre>

The code is valid as it conform to the compiler, however in reality the loop will never exit, and in effect S.O.P will never be executed.

I am using Eclipse Helios IDE for our Web Application development.
Under Problems section in Eclipse, for some of lines the description is displayed as "Dead Code".

Could anybody please tell me what does Dead Code actually mean ?

Please see the screen shot for your reference.

<img src="https://i.stack.imgur.com/vaen2.png" alt="enter image description here">

For example this part is shown as dead code under Eclipse 

<pre><code> else {
 int length;
 if (ar != null)
 length = Array.getLength(ar);
 else
 length = 0; // This line is dead code
</code></pre>

what does Dead Code mean under Eclipse IDE Problems Section

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在使用Eclipse Helios IDE进行Web应用程序开发。在Eclipse中的Problems部分下，某些行的描述显示为"Dead Code“。有人能告诉我Dead Code到底是什么意思吗？请看屏幕截图以供参考。​​例如，这部分在Eclipse下显示为死代码 else {        int length;        if (ar != null)            len

问Eclipse IDE Problems部分下的Dead Code意味着什么
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