Object is the root of the class hierarchy, and each class can have Object as a superclass. All classes directly or indirectly inherit from this class
Constructor method:public Object()
Recall in object-oriented, why is it said that the constructor method of a subclass is accessed by default? Is it the parameterless constructor of the parent class?
Because their top-level parent classes only have no-argument constructors
package com.itheima_56; public class Student extends Object{ private String name; private int age; public Student(){ } public Student(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } //重写toString方法 @Override public String toString() { return "Student{" + "name='" + name + '\'' + ", age=" + age + '}'; } }
package com.itheima_56; /* Object是类层次结构的根,每个类都可以将Object作为超类。所有类都直接或者间接的继承自该类 看方法的源码:选中方法,按下Ctrl+B 建议所有子类重写此方法 如何重写呢?自动生成即可 */ public class ObjectDemo { public static void main(String[] args) { Student s = new Student(); s.setAge(18); s.setName("王昱翔"); System.out.println(s);//默认com.itheima_56.Student@5cad8086 System.out.println(s.toString()); /* public void println(Object x) { //x = s String s = String.valueOf(x); synchronized (this) { print(s); newLine(); } } public static String valueOf(Object obj) { //obj = x; return (obj == null) ? "null" : obj.toString(); } public String toString() { return getClass().getName() + "@" + Integer.toHexString(hashCode()); } */ } }
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