blocks|key|3953209|text|问题是，除了在if(value2.equals(value1))块中之外，您只在int+a;行中声明了它，而从未使用值进行初始化。但是因为if块中的这段代码不能确保运行，所以a可能不会被初始化为传递给b。你可以在声明(或稍后赋值)时用0初始化a：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3953210|int+a+=+0;|code-block|syntax|javascript|3953211|entityMap^0|7|P|14|6|2F|1|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

The problem is that you only declared it in the line <code>int a;</code> but never initialized with a value, besides inside the <code>if(value2.equals(value1))</code> block. But because this code inside the if block can't be sure to run, <code>a</code> might not get initialized to pass to b. You could initialize a with 0 when you declare (or assign a value later):

<pre><code>int a = 0;
</code></pre>

blocks|key|3957641|text|你需要给整型变量a赋值一些默认值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3957642|String+value1+=+"sample";+
String+value2+=+"sample";
int+a+=+0;

try+
{
++++if(value2.equals(value1))
++++{
++++++++a+=+1;
++++}
++++int+b+=+a;

}
catch+(Exception+e)
{
++++System.out.println("Update+Error!");
}|code-block|syntax|javascript|3957643|entityMap^0|8|1|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

You need to assign some default value to int variable <code>a</code>.

<pre><code>String value1 = "sample"; 
String value2 = "sample";
int a = 0;

try 
{
 if(value2.equals(value1))
 {
 a = 1;
 }
 int b = a;

}
catch (Exception e)
{
 System.out.println("Update Error!");
}
</code></pre>

blocks|key|3957805|text|如果你像GMachado说的那样初始化你的变量，你不会得到这个错误，它会在你的try中把值从'a‘传递给'b’。你的代码中也有一个语法错误，在catch之前有一个括号丢失了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3957806|String+value1+=+"sample";+
String+value2+=+"sample";
int+a=0;
try+
{
++++if(value2.equals(value1))
++++{
++++++++a+=+1;
++++}
+++++int+b+=+a;
}+//+Here!!
catch+(Exception+e)
{
++++System.out.println("Update+Error!");
}|code-block|syntax|javascript|3957807|​|3957808|📷|atomic|offset|length|3957809|3957810|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/f190fd01ccb988c45c8bb03fdc09f50c.png|imageAlt^0|0|0|0|0|1|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Z|8|@]|9|@]|A|$]]|$1|I|3|J|5|K|7|10|8|@]|9|@$L|11|M|12|1|13]]|A|$]]|$1|N|3|H|5|6|7|14|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V|W|-4]]]]

If you initialize your variable like GMachado said, you don't get the error, which passes the value from 'a' to 'b' inside your try. You also have a syntax error in your code, there's a bracket missing just before the catch.

<pre><code>String value1 = "sample"; 
String value2 = "sample";
int a=0;
try 
{
 if(value2.equals(value1))
 {
 a = 1;
 }
 int b = a;
} // Here!!
catch (Exception e)
{
 System.out.println("Update Error!");
}
</code></pre>

<a href="https://i.stack.imgur.com/1XuxE.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1XuxE.png" alt="enter image description here"></a>

blocks|key|3958173|text|异常是在出现问题时抛出的东西。您不能简单地期望生成异常。Java中有很多异常。它们都继承自exception类。例如:+ArrayOutOfBoundException，FileNotFoundException，...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3958174|您可以使用throw函数抛出异常。|3958175|容易抛出异常的代码行必须用try/catch括起来。这并不意味着所有内容都应该放在try大括号中。规则是，每当抛出接收时，try+body下的其余行都会被忽略，因为JVM正在寻找catch。|3958176|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Exceptions are somethings that are thrown when something goes wrong. You cannot simply expect to generate an exception. 
There are a lot of exceptions in Java. They all inherit from exception class. IE: ArrayOutOfBoundException, FileNotFoundException,... 

You can use the throw function to throw an exception. 

Lines of code that are prone to throw an exception must be surrounded by try/catch. This does not mean that everything should be within the try curly braces. The rule is that whenever an reception is thrown, the remaining lines under try body is ignored because the JVM is looking for a catch.

How to use a variable from an if-else statement inside Try-Catch in Java?

<pre><code>String value1 = "sample"; 
String value2 = "sample";
int a=0;

try 
{

 if(value2.equals(value1))
 {
 a = 1;
 }
 int b = a;

catch (Exception e)
{
 System.out.println("Update Error!");
}
</code></pre>

The <code>a</code> in <code>int b = a;</code> has an error that says "Variable might not have been initialized". How do I use that variable?

How to use variable from an If-Else statement inside Try-Catch (Java)

Java

如何在Java的Try-Catch中使用if-else语句中的变量？String value1 = "sample"; String value2 = "sample";int a=0;try {    if(value2.equals(value1))    {        a = 1;    }     int ...

问如何在Try-Catch (Java)中使用If-Else语句中的变量
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