Java中实例变量和局部变量未初始化的情况

实例变量会有默认初始值(0,false,null,'\u0000'等)，局部变量不会有默认初始值，

public class test01 {
private String s;
private int [] year = new int[3];

public String getS() {
return s;
}

public void setS(String s) {
this.s = s;
}

public int[] getYear() {
return year;
}

public void setYear(int[] year) {
this.year = year;
}

public static void main(String[] args) {
// TODO Auto-generated method stub
test01 t = new test01();
for(int i=0;i<3;i++)
System.out.println("year[" + i + "] = " + t.getYear()[i]); //代码A
int[] year2 = new int[3];
for(int i=0;i<3;i++)
System.out.println("year2[" + i + "] = " + year2[i]); //代码B
if (t.getS() == null){   //代码C
<span style="white-space:pre">	</span>System.out.println("s is null");
}
String s2;
if (s2 == null){  //代码D
System.out.println("s is null");
}
}

}

代码A处能正常运行，year为实例变量，默认数组内元素都为0：

year[0] = 0

year[1] = 0

year[2] = 0

代码B处能正常运行，因为year2已被初始化，虽然内部元素没有初始化，但都默认为0，内部元素的初始化跟是否是实例变量还是局部变量无关：

year2[0] = 0

year2[1] = 0

year2[2] = 0

代码C处能正常运行，s为String即为对象，默认值为null：

s is null

代码D处有编译错误，S2为局部变量，不会有任何默认值，也不是null值：

The local variable s2 may not have been initialized