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Section 2.10 Worked Example: Call a method of Random

Subgoals for Calling a Method.

  1. Classify method as static method or instance method

    1. If static, use the class name

    2. If instance, must have or create an instance

  2. Write (instance / class) dot method name and ( )

  3. Determine whether parameter(s) are appropriate

    1. Number of parameters passed must match method declaration

    2. Data types of parameters passed must match method declaration (or be assignable)

  4. Determine what the method will return (if anything: data type, void, print, change state of object) and where it will be stored (nowhere, somewhere)

  5. Evaluate right hand side (RHS) of assignment (if there is one). Value is dependent on method’s purpose

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Subsection 2.10.1 Problem Statement

Given the following code, how do you create a Random integer value?

Random rand = new Random();

Subsection 2.10.2 SG1: Classify method as static method or instance method

We already have an instance of Random with the variable name rand.

Subsection 2.10.3 SG2: Write (instance / class) dot method name and ( )

First, check the API to find a method that does what we want.

Figure 2.10.1.
rand.nextInt()

Subsection 2.10.4 SG3: Determine whether parameter(s) are appropriate

According to the API documentation, the nextInt method requires 1 parameter, the exclusive upper bound. If we want to generate random values between 0 to 99 (inclusive) then parameter will be 100.

rand.nextInt(100)

Subsection 2.10.5 SG4: Determine what the method will return (if anything: data type, void, print, change state of object) and where it will be stored (nowhere, somewhere)

According to the API documentation, the nextInt method returns an integer, so we need an int type variable to store the value.

int value = input.nextInt();

Subsection 2.10.6 SG5: Evaluate right hand side (RHS) of assignment (if there is one). Value is dependent on method’s purpose

We used the API documentation to choose the correct parameter, such that the RHS will return an integer between 0 to 99 (inclusive).

int value = input.nextInt();

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