Title: "[[Creating-Java-Classes]]"
Author:
- AllenYGY
status: DONE
tags:
- NOTE
- Java
- Lec3
- Program
created: 2023-11-05T00:59
updated: 2024-05-31T01:01
A class is a programmer-defined type.
A value of a class type is called an object or an instance of the class: an object exhibits the properties and behaviors defined by the object’s class.
Objects have data and behavior.
In java we use constructors to construct new instances.
public ClassName(Parameters){ code }
The new operator is used in combination with constructor to create an object from a particular class.
> ClassName classVar= new ClassName();
In Java, the value of any object variable is a reference [2] to an object that is stored elsewhere.
Person person1 = new Person();
Person person2 = person1;
Person person3 = null; //refers to no object
person1.name // "." is the period operator
person2.age
- instance variables store the data of the object.
- Each object has its own copy of the variables.
- Every object has a state that is determined by the values stored in the instance variables of the object.
A variable declared within a method definition is called a local variable. 定义在方法里的变量
It(this) works as a reference to the current Object, whose method or constructor is being invoked.
public class Person{
private intage;
private String name;
public Person(){
this("Bob",0);
System.out.println("Inside Constructor without parameter");
}
public Person(String name, intage){
this.name = name;
this.age= age;
System.out.println("Inside Constructor with two parameters");
}
}
public class Person {
private intage;
private String name;
public Person(String name, intage)
{
this.name = name;
this.age= age;
}
public void method1(Person pp)
{
System.out.println("Inside Method1");
System.out.println("Age:"+pp.age);
}
public void method2()
{
this.method1(this);
System.out.println("Inside Method2");
}
public static void main(String[] args) {
// TODO Auto-generated method stub
Person p = new Person("Bob",23);
p.method2();
}
}