类的初始化时机
package practise;
class Parent{
static int a =3;
static{
System.out.println("Parent static block");
}
}
class Child extends Parent
{
static int b = 4;
static{
System.out.println("Child static block");
}
}
public class Test4 {
static{
System.out.println("Test4 static block");
}
public static void main(String[] args) {
System.out.println(Child.b);
}
}
Result:
Test4 static block
Parent static block
Child static block
4
package practise;
class Parent5{
static int a =3;
static{
System.out.println("Parent5 static block");
}
}
class Child5 extends Parent5
{
static int b = 4;
static{
System.out.println("Child5 static block");
}
}
public class Test5 {
static{
System.out.println("Test5 static block");
}
public static void main(String[] args) {
Parent5 parent = new Parent5();
System.out.println(Parent5.a);
System.out.println(Child5.b);
}
}
Result:
Test5 static block
Parent5 static block
3
Child5 static block
4
程序中对子类的“主动使用”会导致父类被初始化；但对父类的“主动”使用并不会导致子类
初始化。
调用 ClassLoader类的loadClass方法加载一个类，并不是对类的主动使用，不会导致类的初始化。
package practise;
class C{
static{
System.out.println("Class C");
}
}
public class Test6 {
public static void main(String[] args) {
ClassLoader loader = ClassLoader.getSystemClassLoader();
try {
Class<?> clz = loader.loadClass("practise.C");
System.out.println("----------------");
clz = Class.forName("practise.C");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
Result:
----------------
Class C