如何初始化實體變數(How to initialize instance variable)

方法1:用constructor (建構子)
方法2:用initialize block (初始化區塊)
方法3:用final method

public class InitializeDemo {
    
    
    public static void main(String [] args){
        Student s = new Student();
        System.out.println(s.id);
    }
    
}

class Student{
    
    int id; 
    //Method 1:
    public Student(int id){
        this.id = id;
    }
    
    //Method 2:

    {
        id =1;
    }
    
    //Method 3:
    int phone = initializePhone();
    
    protected int initializePhone(){
        return 3;
    }
    
    public Student(){
        
    }
    
    
    
}

參考自Reference