CHAPTER 4: Types, Values, and Variables

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4.4 Where Types Are Used

Types are used when they appear in declarations or in certain expressions.

The following code fragment contains one or more instances of each kind of usage of a type:

import java.util.Random;

class MiscMath {

	int divisor;


	MiscMath(int divisor) {
		this.divisor = divisor;
	}


	float ratio(long l) {
		try {
			l /= divisor;
		} catch (Exception e) {
			if (e instanceof ArithmeticException)
				l = Long.MAX_VALUE;
			else
				l = 0;
		}
		return (float)l;
	}


	double gausser() {
		Random r = new Random();
		double[] val = new double[2];
		val[0] = r.nextGaussian();
		val[1] = r.nextGaussian();
		return (val[0] + val[1]) / 2;
	}

}

In this example, types are used in declarations of the following:

• Imported types (S7.5); here the type Random , imported from the type java.util.Random of the package java.util , is declared
• Fields, which are the class variables and instance variables of classes (S8.3), and constants of interfaces (S9.3); here the field divisor in the class MiscMath is declared to be of type int
• Method parameters (S8.4.1); here the parameter l of the method ratio is declared to be of type long
• Method results (S8.4); here the result of the method ratio is declared to be of type float , and the result of the method gausser is declared to be of type double
• Constructor parameters (S8.6.1); here the parameter of the constructor for MiscMath is declared to be of type int
• Local variables (S14.3, S14.12); the local variables r and val of the method gausser are declared to be of types Random and double[] (array of double )
• Exception handler parameters (S14.18); here the exception handler parameter e of the catch clause is declared to be of type Exception

and in expressions of the following kinds:

• Class instance creations (S15.8); here a local variable r of method gausser is initialized by a class instance creation expression that uses the type Random
• Array creations (S15.9); here the local variable val of method gausser is initialized by an array creation expression that creates an array of double with size 2
• Casts (S15.15); here the return statement of the method ratio uses the float type in a cast
• The instanceof operator (S15.19.2); here the instanceof operator tests whether e is assignment compatible with the type ArithmeticException