Java中类的初始化顺序
一.测试单类的初始化顺序
public class ClassInitOrderTest {
//静态变量
public static String staticField = "static field";
//静态代码块
static {
System.out.println(staticField);
System.out.println("static block");
}
//成员变量
private String field = "member field";
//非静态代码块
{
System.out.println(field);
System.out.println("non-static block");
}
//构造器
public ClassInitOrderTest() {
System.out.println("constructor");
}
public static void main(String[] args) {
new ClassInitOrderTest();
}
}
程序输出结果:
static field
static block
member field
non-static block
constructor
结论:
静态变量 > 静态初始块 > 成员变量 > 非静态初始块 > 构造器
二.测试继承中类的初始化顺序
class Parent {
//父类静态变量
private static String parentStaticField = "parent static field";
//父类静态代码块
static {
System.out.println(parentStaticField);
System.out.println("parent static block");
}
//成员变量
private String parentField = "parent member field";
//非静态代码块
{
System.out.println(parentField);
System.out.println("parent non-static block");
}
//父类构造器
public Parent() {
System.out.println("parent constructor");
}
}
public class Child extends Parent {
//子类静态变量
private static String childStaticField = "child static field";
//子类静态代码块
static {
System.out.println(childStaticField);
System.out.println("child static block");
}
//子类成员变量
private String childField = "child member field";
//子类非静态代码块
{
System.out.println(childField);
System.out.println("child non-static block");
}
//子类构造器
public Child() {
System.out.println("child constructor");
}
public static void main(String[] args) {
new Child();
}
}
输出结果:
parent static field
parent static block
child static field
child static block
parent member field
parent non-static block
parent constructor
child member field
child non-static block
child constructor
结论:
父类静态变量 > 父类静态初始块 > 子类静态变量 > 子类静态初始块 > 父类成员变量 > 父类非静态初始块 > 父类构造器 > 子类成员变量 > 子类非静态初始块 > 子类构造器