The construction method of Java Foundation and its application

• A constructor method is a special method that is a method that has the same name as the class and no return value type (even void) .
• The creation of an object is accomplished by means of a construction method, whose function is to initialize the object .
• Constructor methods are called automatically when a class instantiates an object. Construction methods can be overloaded as well as other methods.
• There are two kinds of construction methods: The method of constructing method with no parameters
• Class must have a construction method, if not written, the system automatically add a non-parametric structure. (Interfaces cannot be instantiated, so there is no construction method in the interface.) ）

Example Demo: Calculate the distance from a coordinate point

Entity class Point Code:

1  Public classPoint {2 3     //properties of points horizontal ordinate4     intx;5     inty;6     7     //default no parameter constructor8      PublicPoint () {9SYSTEM.OUT.PRINTLN ("Default construct. ");Ten     } One      A     //The structure of the reference 1 -      PublicPoint (intAintb) { -System.out.println ("with a reference structure. "); the         //Assigning a value to an object -x =A; -y =b; -     } +     //Parametric Construction 2 (heavy duty) -      PublicPoint (inta) { + //System.out.println (); A          This(A,a);//the overloaded call above has the parameter construct 1 (this syntax is specifically used to construct a call between methods and must be written on the first line of the constructor method) at     } -      -     /** - * Calculation method of point distance - * Parameters are: Non-point sitting punctuation object - * Method Overloading in      */ -      Public DoubleDistance () {//No reference to         returnMath.sqrt (Math.pow ( This. x, 2) + Math.pow ( This. Y, 2));//the distance from the original point +     } -      the     //the distance to a point *      Public DoubleDistanceintAintb) {//parameter is point coordinate $         returnMath.sqrt (Math.pow ( This. X-a, 2) +math.pow ( This. Y-b, 2));Panax Notoginseng     } -      the      Public DoubleDistance (point P) {//parameter is a point object +         returndistance (p.x, p.y); A     } the      +}

Demo:

1  Public classPointdemo {2      Public Static voidMain (string[] args) {3         4Point P1 =NewPoint (3,2);5System.out.println ("p1" coordinates are: "+" ("+ p1.x +", "+ P1.y +") ");6         7Point P2 =NewPoint (5);8System.out.println ("p2" coordinates are: "+" ("+ p2.x +", "+ P2.y +") ");9         Ten         /** One * To find the distance to the point A          */ -Point P =NewPoint (6,8); -System.out.println ("Distance to Origin:" + p.distance ());//the distance from the original point theSystem.out.println ("Distance to another point is:" + p.distance (3, 3));//distance to (3,3) -System.out.println ("The distance to a point object is:" + p.distance (p2));//distance to point object P2 -     } -}

The output is:

There is a reference structure.
The coordinates of P1 are: (3,2)
There is a reference structure.
The coordinates of P2 are: (5,5)
There is a reference structure.
The distance from the origin point is: 10.0
Distance to another point is: 5.830951894845301
The distance to a point object is: 3.1622776601683795

The construction method of Java Foundation and its application