CircleCalculator constructor 4. public CircleCalculator ( constructor radius 0.0; prototype area 0.0; circumference 0.0; later we will see that constructors can have Here we just assign values of zero for each arguments data field.The actual radius will be obtained using the readlnput method and the area and circumference will be calculated using the doCalculations method. Programming in Java JAVA
4-11 Programming in Java CircleCalculator constructor public CircleCalculator() { radius = 0.0; area = 0.0; circumference = 0.0; } Here we just assign values of zero for each data field. The actual radius will be obtained using the readInput method and the area and circumference will be calculated using the doCalculations method. later we will see that constructors can have arguments constructor prototype
readInput method public void readInput ( method prototype KeyboardReader input new KeyboardReader () System.out.println("Enter radius"); constructo radius input.readDouble(); all expression method call Note: expressions 一种可能的错误 double radius = input.readDouble () 将radius定义成局部变量 Programming in Java JAVA
4-12 Programming in Java readInput method public void readInput() { KeyboardReader input = new KeyboardReader(); System.out.println("Enter radius"); radius = input.readDouble(); } Note: 一种可能的错误 double radius = input.readDouble(); 将radius定义成局部变量 method prototype method call expressions constructo r call expression
a2水 doCalculations method 4-13 method public void doCalculations ( prototype area Math.PI radius radius; circumference 2.0 Math.PI radius; } these are data field variables and they are not declared here 兰 Programming in Java
4-13 Programming in Java doCalculations method public void doCalculations() { area = Math.PI * radius * radius; circumference = 2.0 * Math.PI * radius; } these are data field variables and they are not declared here method prototype
a2水 displayResults method 4-14 method prototype public void displayResults() System.out.println ("Radius:"radius); System.out.println ("Area:"area); System.out.println ("Circumference: circumference); } three are method call expressions Programming in Java JAVA
4-14 Programming in Java displayResults method public void displayResults() { System.out.println("Radius: " + radius); System.out.println("Area: " + area); System.out.println("Circumference: " + circumference); } method prototype three are method call expressions
a2水 Objects and Messages (1) 4-15 object to The dot separates receive object name message from message name radius input.readDouble(); Assign result Method that sends to a double message to object variable Programming in Java JAVA
4-15 Programming in Java Objects and Messages (1) radius = input.readDouble(); object to receive message Method that sends message to object Assign result to a double variable The dot separates object name from message name