blocks|key|227320|text|可以，实例变量将被初始化为默认值。对于局部变量，您需要在使用前进行初始化：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|227321|public+class+Main+{

++++int+instaceVariable;+//+An+instance+variable+will+be+initialized+to+the+default+value

++++public+static+void+main(String[]+args)+{
++++++++int+localVariable+=+0;+//+A+local+variable+needs+to+be+initialized+before+use
++++}
}|code-block|syntax|javascript|227322|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|$]]

Yes, an instance variable will be initialized to a default value. For a local variable, you need to initialize before use:
<pre><code>public class Main {

 int instaceVariable; // An instance variable will be initialized to the default value

 public static void main(String[] args) {
 int localVariable = 0; // A local variable needs to be initialized before use
 }
}
</code></pre>

blocks|key|10807|text|在第一个代码示例中，a是一个main方法局部变量。方法局部变量需要在使用前进行初始化。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|10808|在第二个代码示例中，a是类成员变量，因此它将被初始化为默认值。|10809|entityMap^0|A|1|E|4|0|A|1|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|R|8|@]|D|@]|E|$]]]|I|$]]

In the first code sample, <code>a</code> is a <code>main</code> method local variable. Method local variables need to be initialized before using them.
In the second code sample, <code>a</code> is class member variable, hence it will be initialized to the default value.

blocks|key|10838|text|所有成员变量都必须加载到堆中，因此在创建类的实例时必须使用默认值进行初始化。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|10839|如果是局部变量，它们不会被加载到堆中。它们一直存储在堆栈中，直到被使用为止。这是在Java+7之前，所以我们需要显式地初始化它们。|10840|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

All member variables have to load into the heap, so they have to be initialized with default values when an instance of class is created.
In case of local variables, they don't get loaded into the heap. They are stored on the stack until they are being used. This is before Java 7, so we need to explicitly initialize them.

blocks|key|10858|text|在Java中，默认初始化只适用于类member的实例变量。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|10859|它不适用于局部变量。|10860|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

In Java, the default initialization is applicable for only instance variable of class member.
It isn't applicable for local variables.

blocks|key|10907|text|局部变量不会获得默认值。如果不通过某种方式赋值，它们的初始值是未定义的。在使用局部变量之前，必须先对其进行初始化。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|10908|当你在类级别(作为成员，即字段)和方法级别声明变量时，会有很大的不同。|10909|如果您在类级别声明一个字段，它们将根据其类型获取默认值。如果你在方法级别声明一个变量或声明为一个块(意味着{}中的任何代码)，不要获取任何值，并且保持未定义，直到它们以某种方式获得一些起始值，即分配给它们的一些值。|10910|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|$]]

Local variables do not get default values. Their initial values are undefined without assigning values by some means. Before you can use local variables they must be initialized.
There is a big difference when you declare a variable at class level (as a member, i.e., as a field) and at the method level.
If you declare a field at the class level they get default values according to their type. If you declare a variable at the method level or as a block (means any code inside {}) do not get any values and remain undefined until somehow they get some starting values, i.e., some values assigned to them.

blocks|key|10959|text|在第一种情况下，您将"int+a“声明为局部变量(在方法中声明)，而local+varible不获取默认值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|10960|但是实例变量被赋予了静态和非静态的默认值。|10961|实例变量的默认值：|10962|int+=0|10963|浮点数，双精度=+0.0|10964|引用变量=+null|10965|char+=0(空格字符)|10966|boolean+=+false|10967|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|V|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|W|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|X|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|Y|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|Q|$]]

In the first case you are declaring &quot;int a&quot; as a local variable(as declared inside a method) and local varible do not get default value.
But instance variable are given default value both for static and non-static.
Default value for instance variable:
int = 0
float,double = 0.0
reference variable = null
char = 0 (space character)
boolean = false

Based on <a href="http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html" rel="noreferrer">my reference</a>, primitive types have default values and Objects are null. I tested a piece of code.
<pre><code>public class Main {
 public static void main(String[] args) {
 int a;
 System.out.println(a);
 }
}
</code></pre>
The line <code>System.out.println(a);</code> will be an error pointing at the variable <code>a</code> that says <code>variable a might not have been initialized</code> whereas in the given reference, <code>integer</code> will have <code>0</code> as a default value. However, with the given code below, it will actually print <code>0</code>.
<pre><code>public class Main {
 static int a;
 public static void main(String[] args) {
 System.out.println(a);
 }
}
</code></pre>
What could possibly go wrong with the first code? Do class variables behave different from local variables?

Default values and initialization in Java

基于，基元类型具有默认值，而对象为空。我测试了一段代码。public class Main {    public static void main(String[] args) {        int a;        System.out.println(a);    }}行System.out.println...

问Java中的默认值和初始化
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