Codehs 1.6.4 Casting To An Int
Jeannine Lander
You'll likely get 2. However, I am wondering: since double representations of integers sometimes look like 1.9999999998 or something, is there a possibility that casting a double created via Math.round() will still result in a truncated down number, rather than the rounded number we are looking for (i.e.: 1 instead of 2 in the code as represented) ?
No, round() will always round your double to the correct value, and then, it will be cast to an long which will truncate any decimal places. But after rounding, there will not be any fractional parts remaining.
Returns the closest long to the argument. The result is rounded to an integer by adding 1/2, taking the floor of the result, and casting the result to type long. In other words, the result is equal to the value of the expression:
The casting operators (int) and (double) are used right next to a number or variable to create a temporary value converted to a different data type. For example, (double) 1/3 will give a double result instead of an int one. Run this code to find how Java handles division and what casting can do to the results. Notice what happens when you divide an int by an int or an int by a double or an int casted to a double divided by an int.
Java assumes that if you are doing division with integers that you want an integer result and it will truncate and throw away the part after the decimal point. But, if you use a mixture of integers (int) and decimal (double) numbers Java will assume that you want a double result. If there is at least one double in the operation, Java will widen the type of the other operand to double too and return the result in a double. If you have integers and you want a double result from some mathematical operation cast one of the integers to a double using (double) as shown above.
For example, int values are stored in 4 bytes of memory. There is an Integer.MAX_VALUE defined as 2147483647 and an Integer.MIN_VALUE defined as -2147483648. If you try to store any number larger or smaller than these numbers in an int variable, it will result in an error called integer overflow. Try it below.
In the code below, declare and initialize 3 int variables that represent grades, and then sum and average them.Use casting to report the result as a double.For example, if the grades are 90, 100, and 94, the sum of the threenumbers is 90 + 100 + 94 = 284, and the average is the sum 284 divided by 3 whichcasted to a double is 94.666667. You should use variables instead of the numeric literalsin your formulas. Follow the pseudocode below.
Sum and average 3 grades. Your grade variables must have type int, not double.Use type casting to compute the average as a double.For an extra challenge, use a Scanner to read the grades from standard input.
Integer values in Java are represented by values of type int, which are stored using a finite amount (4 bytes) of memory. Therefore, an int value must be in the range from Integer.MIN_VALUE to Integer.MAX_VALUE inclusive.
Base codes consist of a letter (A-Z, some letters are omitted) followed by a two-digit number. The letter refers to the year of manufacture, while the number refers to the week number (1-52, 53 is rarely used and only can be found during leap years) within that year.
For example, if the code is "M36", the letter "M" indicates that the car was manufactured in 2019, and the number "36" indicates the car was manufactured on the 36th week of that year. This puts the production date around the first week of September 2019 (2 to 8 September).
These production codes consist of a four-digit number followed by a two- or three-letter code. The four-digit number refers to the day and year of manufacture and the two- or three-letter code refers to the plant which the car is produced in. The following is an example.
These date codes have no real significance except for the possibility of a recall indicator as it can identify when a particular casting was in production at the manufacturing plant or to identify tooling changes between castings (e.g. base variations).
Production of a full batch of 15 mixes of Hot Wheels cars generally takes about a year; models in a given year's first mix generally begin production in late July or early August of the previous year (with a little bit of last year's last mix overflowing into the first mix of the current year), with the final mix being produced around mid-July (with the same overflow into next year's first mix). The first mix of a given year is generally put out in stores in September of the previous year (e.g. 2023 mixes released in September 2022), with the last in August the next year; this can vary from country to country. This is why the initial few mixes of Hot Wheels cars for a given year feature base codes corresponding to dates from the previous year.
Variables are memory containers used to store information. In Java, every variable has a data type and stores a value of that type. Data types, or types for short, are divided into two categories: primitive and non-primitive. There are eight primitive types in Java: byte, short, int, long, float, double, boolean and char. These built-in types describe variables that store single values of a predefined format and size. Non-primitive types, also known as reference types, hold references to objects stored somewhere in memory. The number of reference types is unlimited, as they are user-defined. A few reference types are already baked into the language and include String, as well as wrapper classes for all primitive types, like Integer for int and Boolean for boolean. All reference types are subclasses of java.lang.Object [1].
In programming, it is commonplace to convert certain data types to others in order to allow for the storing, processing, and exchanging of data between different modules, components, libraries, APIs, etc. Java is a statically typed language, and as such has certain rules and constraints in regard to working with types. While it is possible to convert to and from certain types with relative ease, like converting a char to an int and vice versa with type casting [2], it is not very straightforward to convert between other types, such as between certain primitive and reference types, like converting a String to an int, or one user-defined type to another. In fact, many of these cases would be indicative of a logical error and require careful consideration as to what is being converted and how, or whether the conversion is warranted in the first place. Aside from type casting, another common mechanism for performing type conversion is parsing [3], and Java has some predefined methods for performing this operation on built-in types.
The incompatible types error indicates a situation where there is some expression that yields a value of a certain data type different from the one expected. This error implies that the Java compiler is unable to resolve a value assigned to a variable or returned by a method, because its type is incompatible with the one declared on the variable or method in question. Incompatible, in this context, means that the source type is both different from and unconvertible (by means of automatic type casting) to the declared type.
This might seem like a syntax error, but it is a logical error discovered in the semantic phase of compilation. The error message generated by the compiler indicates the line and the position where the type mismatch has occurred and specifies the incompatible types it has detected. This error is a generalization of the method X in class Y cannot be applied to given types and the constructor X in class Y cannot be applied to given types errors discussed in [4].
The incompatible types error most often occurs when manual or explicit conversion between types is required, but it can also happen by accident when using an incorrect API, usually involving the use of an incorrect reference type or the invocation of an incorrect method with an identical or similar name.
Assigning a value of one primitive type to another can happen in one of two directions. Either from a type of a smaller size to one of a larger size (upcasting), or from a larger-sized type to a smaller-sized type (downcasting). In the case of the former, the data will take up more space but will be intact as the larger type can accommodate any value of the smaller type. So the conversion here is done automatically. However, converting from a larger-sized type to a smaller one necessitates explicit casting because some data may be lost in the process.
Parsing is a more complex process than type casting as it involves analyzing the underlying structure of a given data before converting it into a specific format or type. For instance, programmers often deal with incoming streams of characters, usually contained in a string that needs to be converted into specific types to make use of in the code. A common scenario is extracting numeric values from a string for further processing, which is where parsing is routinely used.
Popular external libraries are also prone to naming their reference types similarly, so whenever relying on such a library for a certain feature or functionality it is important to pick one, or be careful not to confuse one for another, if multiple libraries are already being used.
Fig. 6(a) shows an example of passing a JSON type object to a method as an argument. Here, the method printJson expects an argument of type JsonObject, but the calling method tries to pass in an instance of the similarly named JSONObject reference type, part of a different library altogether. This results in the incompatible types error being raised by the compiler, with the alert org.json.JSONObject cannot be converted to javax.json.JsonObject pointing to the erroneous method call. Swapping the inappropriate constructor call with an instance of the correct type solves the issue, as shown in Fig. 6(b).
Fig. 6 also serves as an example to show how the incompatible types error is, in fact, a generalization of the method X in class Y cannot be applied to given types error explored in [4]. Depending on the specific compiler that is being used and its configuration settings, either of these errors could be triggered in this kind of scenario.
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