Java-类型初始化

灰太狼 2021-09-29 02:24 288阅读 0赞

当变量只定义不赋值，不一样的类型会有不同的初始值

1，**基础数据类型**

1.1 **代码**：

package com.company;
    
    public class Main {
    
        static byte b;
        static short s;
        static int i;
        static long l;
        static float f;
        static double d;
        static char c;
        static boolean bool;
    
        public static void main(String[] args) {
            System.out.print("byte=" + b +",");
            System.out.print("short=" + s +",");
            System.out.print("int=" + i +",");
            System.out.print("long=" + l +",");
            System.out.print("float=" + f +",");
            System.out.print("double=" + d +",");
            System.out.print("char=" + c +",");
            System.out.print("boolean=" + bool);
        }
    }

1.2 **结果**：

byte=0,short=0,int=0,long=0,float=0.0,double=0.0,char= ,boolean=false

1.3 **结论**：

<table style="width:500px;"> 
 <tbody> 
  <tr> 
   <td> <pre>byte</pre> </td> 
   <td> <pre>short</pre> </td> 
   <td> <pre>int</pre> </td> 
   <td> <pre>long</pre> </td> 
   <td> <pre>float</pre> </td> 
   <td> <pre>double</pre> </td> 
   <td> <pre>char</pre> </td> 
   <td> <pre>boolean</pre> </td> 
  </tr> 
  <tr> 
   <td>0</td> 
   <td>0</td> 
   <td>0</td> 
   <td>0</td> 
   <td> <p>0.0</p> </td> 
   <td>0.0</td> 
   <td>&nbsp;</td> 
   <td>false</td> 
  </tr> 
 </tbody> 
</table>

2，**引用类型**：

2.1 **代码**

package com.company;
    
    public class Main {
    
        static Byte b;
        static Short s;
        static Integer i;
        static Long l;
        static Float f;
        static Double d;
        static Character c;
        static Boolean bool;
        static String str;
    
        public static void main(String[] args) {
            System.out.print("Byte=" + b +",");
            System.out.print("Short=" + s +",");
            System.out.print("Integer=" + i +",");
            System.out.print("Long=" + l +",");
            System.out.print("Float=" + f +",");
            System.out.print("Double=" + d +",");
            System.out.print("Character=" + c +",");
            System.out.print("Boolean=" + bool +",");
            System.out.print("String=" + str);
        }
    }

2.2 **结果**

Byte=null,Short=null,Integer=null,Long=null,Float=null,Double=null,Character=null,Boolean=null,String=null

2.3 **结论**

引用类型只定义不赋值时，初始化为null

3，**局部变量中定义**

3.1 **代码**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxMTUwMzY1_size_16_color_FFFFFF_t_70][]

3.2 **结论**

局部变量需要定义初始值，才能使用

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxMTUwMzY1_size_16_color_FFFFFF_t_70]: /images/20210923/dc80797d1e1d43b4905f14ac17ef2b29.png