Java constructors, building blocks of code, execution order of static code blocks

Constructors

With the same name as the class and no return value, used to initialize class properties;

The constructor is also divided into the parameterless constructor and the parametric constructor.

1.1: No parameter constructor

public class contruction{//... Properties ... public contruction () {}//No parameter constructor, no write, the system will automatically add}

1.2: A parametric constructor

public class Contruction {private int i; public contruction (int i) {/* has a parameter constructor, if you define a constructor with parameters,    you must have parameters when instantiating the object, otherwise you will get     an error because you created a parameter,　　　　Then you know exactly what you're doing. The system does not automatically add the parameterless constructor */this.i = i; }}

Building Code Blocks

An instantiation of an object executes once per instantiation;

The code block is constructed in the following format:

public class Contruction {public    contruction () {        System.out.pintln ("I am a constructor method");    }    {        System.out.pintln ("I am Building code block");    }    public static void Main (String args[]) {         contruction c1=new contruction ();         contruction c2=new contruction ();           } }   

Results:

As you can see from the results, constructing code blocks takes precedence over constructors.

Static code block

Class loading executes, regardless of the number of new objects, executed only once;

public class Contruction {public    contruction () {        System.out.println ("I am a constructor method");    }    static {        System.out.println ("I am a static code block. No matter how many instances of new, I only execute once ");    }    public static void Main (String args[]) {         contruction c1 = new contruction ();         contruction C2 = new contruction ();}     }

Results:

As you can see from the results, the static code block executes only once and takes precedence over the constructor execution.

No inherited initialization order:

Static member variables, static code blocks >> Normal member variables, plain code blocks >> constructors

Has an inherited initialization order:

Parent class static member variable, parent class static code block >> subclass static member variable, static code block >> parent class normal member variable, parent class code block >> parent class constructor >> subclass ordinary member variable, subclass generic code Blocks >> sub-class constructors

Java constructors, building blocks of code, execution order of static code blocks