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看了Thinking In Java这本书,对于静态代码块,匿名代码块,无参构造器和有参构造器,上边对这部分讲的比较乱,整理一下:
class Cups{
Cups(int i){
System.out.println("This is a parameter constructor"+i);
}
Cups(){
System.out.println("This is a non parameter constructor");
}
{
System.out.println("This is an anonymous code block");
}
static{
System.out.println("This is a static code block");
}
}
public class AnonymousConstructor {
public static void main(String[] args) {
new Cups();
new Cups(1);
}
}
执行结果为:
This is a static code block //静态代码块最先执行,而且只执行一次
This is an anonymous code block //匿名代码块在每次构造器初始化前都会执行
This is a non parameter constructor //有参和无参构造器的执行顺序与被调用的次序相同
This is an anonymous code block //匿名代码块在每次构造器初始化前都会执行
This is a parameter constructor1
如果代码块换成类对象的初始化,执行结果也是一样的,例如:
class Cup{
Cup(){
System.out.println("This is a Cup constructor");
}
}
class Cups{
Cups(int i){
System.out.println("This is a parameter constructor"+i);
}
Cups(){
System.out.println("This is a non parameter constructor");
}
{
System.out.println("This is an anonymous code block");
}
static{
System.out.println("This is a static code block");
new Cup();
}
}
public class AnonymousConstructor {
public static void main(String[] args) {
new Cups();
new Cups(1);
}
}
这段代码增加了一个辅助的类Cup,然后在静态代码块中调用,执行结果:
This is a static code block
This is an anonymous code block
This is a non parameter constructor
This is an anonymous code block
This is a parameter constructor1