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This class named Graph01Demo is used to demonstrate how to write data-generator classes that will operate successfully with the program named Graph01 .
( Figure 1 shows the display of the data produced by this class. You might want to refer to that figure while examining the code in this class.)
Listing 2 shows the beginning of the class definition, which names the class Graph01Demo , and specifies that the class implements the interface named GraphIntfc01 .
| Listing 2. Beginning of the class named Graph01Demo. |
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class Graph01Demo implements GraphIntfc01{ |
Listing 3 shows the entire listing of the method named getNmbr .
| Listing 3. The method named getNmbr. |
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public int getNmbr(){
return 5;}//end getNmbr |
Recall from the earlier discussion that the method named getNmbr must return an integer value between 1 and 5, which tells the plotting programnamed Graph01 how many functions to plot.
This demonstration plots all five functions, as shown in Figure 1 , so this method returns the value 5.
Listing 4 shows the entire method named f1 . The output from this method is plotted in the topmost plotting area of the display in Figure 1 . (This is the area at the top with the white background.)
| Listing 4. The method named f1. |
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public double f1(double x){
return -(x*x)/200.0;}//end f1 |
This method receives an incoming parameter known locally as x . (Computations are performed on the fly by all five data-generator methods defined in this class.) The method computes and returns the negative square of the incoming parameter (divided by 200) . This produces the inverted bowl shape at the top of Figure 1 .
The curve plotted in the top-most plotting area with the gray background in Figure 1 is produced by the method named f2 , which is shown in its entirety in Listing 5 .
| Listing 5. The method named f2. |
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public double f2(double x){
return -(x*x*x)/200.0;}//end f2 |
As before, this function receives an incoming parameter known locally as x . The function computes and returns the negative cube of the incoming parameter (divided by 200) . This produces the curve shown in the top-most gray area of Figure 1 .
The method named f3 , shown in Listing 6 , produces the curve shown in the center plotting area with the white background in Figure 1 .
| Listing 6. The method named f3. |
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public double f3(double x){
return 100*Math.cos(x/10.0);}//end f3 |
This is a simple cosine curve, which is computed on the fly. Each time the method is called, the incoming parameter named x is used to calculate the cosine of an angle in radians given by one-tenth the value of x . The cosine of that angle is multiplied by 100 and returned.
(Note that the cosine of the angle is computed using a static method of the standard Java class named Math . This is the class that contains the Java math library.)
The curve shown in the bottom-most gray plotting area of Figure 1 is produced by the method named f4 , shown in Listing 7 .
| Listing 7. The method named f4. |
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public double f4(double x){
return 100*Math.sin(x/20.0);}//end f4 |
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