对象构造和初始化

（1）构造方法
对象都有构造方法，如果没有，则添加一个default方法
抽象类有构造方法

（2）调用本类和父类
this 本类其他
super父类
父类所有构造方法都得到调用
例：

class A{    A(int a){}}class B extends A{    B(String s){} //不能通过编译}

1.class A{       A(){}       A(int a){}}2.class A{}3.class B extends A{    super(3);    B(String s){}}

（3）创建对象时初始化

p = new Person(){{age = 18; name = ' '}}

（4）构造方法执行过程
先父类构造，再本类赋值，最后执行构造方法中的语句

public class MyDate {    public static void main(String[] args){         Person p = new Student("B", 18, "Q");    }}class Person{    String name="A";  //step 2    int age=-1;   Person(String name, int age)   {        super(); //step 1        //step 3        System.out.println( "this.name="+this.name+",this.age="+this.age );        this.name=name; this.age=age;         System.out.println( "Person() this.name="+this.name+",this.age="+this.age );    }}class Student extends Person{    String school="PKU"; //step2     Student( String name, int age, String school )    {        super( name, age );  //step 1        //step 3        System.out.println( "this.name="+this.name+",this.age="+this.age+",this.school="+this.school );        this.school = school;        System.out.println( "Student() this.name="+this.name+",this.age="+this.age+",this.school="+this.school );    }}结果：this.name=A,this.age=-1Person() this.name=B,this.age=18this.name=B,this.age=18,this.school=PKUStudent() this.name=B,this.age=18,this.school=Q