Getting Started with Java_Chapter 5_Practice Exercises 5_4

Creation of "calc Triangle Area" and "calc Circle Area" according to the specifications

Specification:

| | | |:-----------------|:------------------|　　　　　 |Method name|calcTriangleArea| |Return type|Triangle area(double)| |1st argument|The length of the base of the triangle, the unit is cm(double bottom)| |2nd argument|The height of the triangle, the unit is cm(double height)| |Processing content|Use the argument to find the area and return it.|

| | | |:-----------------|:------------------|　 |Method name|calcCircleArea| |Return type|Area of a circle(double)| |1st argument|The radius of the circle, the unit is cm(double bottom)| |Processing content|Use the argument to find the area and return it.|

answer

Main.java

1  public class Main {
2      public static double calcTriangleArea(double bottom, double height){
3          double area = (bottom * height) / 2;
4          return area;
5      }
6      public static double calcCircleArea(double radius){
7          double area = radius * radius * 3.14;  
8          return area;
9      }
10     public static void main(String[] args){
11         double triangleArea = calcTriangleArea(10.0, 5.0);
12         System.out.println("Triangle area:" + triangleArea + "Square cm");
13         double circleArea = calcCircleArea(5.0);
14         System.out.println("Area of a circle:" + circleArea + "Square cm");
15     }
16 }

Main.java_console

Triangle area:25.0 square cm
Area of a circle:78.5 square cm

Programming order

① Make sure to check the specifications. ② "class" is created in Main. ③ Create a method of "calcTriangleArea". ④ Create a method of "calcCircleArea". ⑤ Create a "call method" in main. ⑥ Compile. ⑦ Confirmation, end.

Creating a class

class Main

Main.java

1  public class Main {

Method definition

calcTriangleArea

Main.java

2  public static double calcTriangleArea(double bottom, double height){
3      double area = (bottom * height) / 2;
4      return area;
5  }

(1) Create an equation to find the area of the triangle.

② public static ``` return value is ** double (because floating point is used) **, method name` `` is specified ** calcTriangle Describe Area **.

③ In (), pass the `` `argument ``` ** double bottom, double height **.

④ Next, describe the calculation formula. double area = (bottom * height) / 2; ** [Variable type Arbitrary variable name = (base x height) ÷ 2;] **.

⑤ , return is used to pass the assigned double area to the return value double. Write ** return area; **.

calcCircleArea

Main.java

6  public static double calcCircleArea(double radius){
7      double area = radius * radius * 3.14 ;     
8      return area;         
9  }        

(1) Create a formula to calculate the area of a circle.

② public static `return value ``` is ** double (because floating point is used) **, method name `` is specified ** calcCircle Describe Area **.

③ In (), pass the ``` argument ** double radius **.

④ Next, describe the calculation formula.

double area = radius * radius * 3.14;

 ** [Variable type Arbitrary variable name = radius x radius x pi;] **.

 ⑤ `return is used to pass the assigned double area to the return value double.
 Write ** return area; **.



# Call and output to screen
### Main method

#### **`Main.java`**
```java

10  public static void main(String[] args){
11      double triangleArea = calcTriangleArea(10.0, 5.0);
12      System.out.println("Triangle area:" + triangleArea + "Square cm");
13      double circleArea = calcCircleArea(5.0);
14      System.out.println("Area of a circle:" + circleArea + "Square cm");
15  }
16 }

(1) Create a Main method to call and output to the screen.

(2) public static return value is ** void (no return value) **, method name is ** Main **, and () is Write ** String [] args **.

③ Next, call the method, pass the value, and assign it to the left side. From calcTriangleArea, in order Call.

④double triangleArea = calcTriangleArea(10.0, 5.0); ** [Variable type Arbitrary variable name = Method name (base, height)] **.

• In calcTriangleArea (10.0, 5.0), call the definition, pass ** values 10.0 and 5.0 to the argument (), and double Substitution to triangleArea ** is done collectively.
• ÷ 2 is defined by the calcTriangleArea method, so no description is required.

⑤ In Sytem.out.println () ;, if you write ** "triangle area:" + triangleArea + "square cm" ** in (), Output to the screen.

⑥ Next, call calcCircleArea, pass the ** value, and assign it to the left side **.

⑦double circleArea = calcCircleArea(5.0); ** [Variable type arbitrary variable name = method name (radius)] **.

• In calcCircleArea (5.0), the definition is called, ** value 5.0 is passed to argument (), and it is assigned to double circleArea **.
• Only one 5.0 is passed as the value, but it is defined by the calcCircleArea method. So no description is needed.

⑧ In Sytem.out.println () ;, if you write ** "area of a circle:" + circleArea + "square cm" ** in (), Output to the screen.

When compiled (screen output)

Main.java_console

Triangle area:25.0 square cm
Area of a circle:78.5 square cm

-Becomes.

that's all.

Summary

I tried to summarize how to create "calcTriangleArea" and "calcCircleArea" according to the specifications of Java Introduction-Chapter 5-Practice Exercises 5-4.

References

A refreshing introduction to Java-Second Edition-Impress Publishing, Inc. Kiyotaka Nakayama / Daigo Kunimoto