Math abs java что это
Unlike some of the numeric methods of class StrictMath , all implementations of the equivalent functions of class Math are not defined to return the bit-for-bit same results. This relaxation permits better-performing implementations where strict reproducibility is not required.
By default many of the Math methods simply call the equivalent method in StrictMath for their implementation. Code generators are encouraged to use platform-specific native libraries or microprocessor instructions, where available, to provide higher-performance implementations of Math methods. Such higher-performance implementations still must conform to the specification for Math .
The quality of implementation specifications concern two properties, accuracy of the returned result and monotonicity of the method. Accuracy of the floating-point Math methods is measured in terms of ulps, units in the last place. For a given floating-point format, an ulp of a specific real number value is the distance between the two floating-point values bracketing that numerical value. When discussing the accuracy of a method as a whole rather than at a specific argument, the number of ulps cited is for the worst-case error at any argument. If a method always has an error less than 0.5 ulps, the method always returns the floating-point number nearest the exact result; such a method is correctly rounded. A correctly rounded method is generally the best a floating-point approximation can be; however, it is impractical for many floating-point methods to be correctly rounded. Instead, for the Math class, a larger error bound of 1 or 2 ulps is allowed for certain methods. Informally, with a 1 ulp error bound, when the exact result is a representable number, the exact result should be returned as the computed result; otherwise, either of the two floating-point values which bracket the exact result may be returned. For exact results large in magnitude, one of the endpoints of the bracket may be infinite. Besides accuracy at individual arguments, maintaining proper relations between the method at different arguments is also important. Therefore, most methods with more than 0.5 ulp errors are required to be semi-monotonic: whenever the mathematical function is non-decreasing, so is the floating-point approximation, likewise, whenever the mathematical function is non-increasing, so is the floating-point approximation. Not all approximations that have 1 ulp accuracy will automatically meet the monotonicity requirements.
The platform uses signed two’s complement integer arithmetic with int and long primitive types. The developer should choose the primitive type to ensure that arithmetic operations consistently produce correct results, which in some cases means the operations will not overflow the range of values of the computation. The best practice is to choose the primitive type and algorithm to avoid overflow. In cases where the size is int or long and overflow errors need to be detected, the methods addExact , subtractExact , multiplyExact , and toIntExact throw an ArithmeticException when the results overflow. For other arithmetic operations such as divide, absolute value, increment, decrement, and negation overflow occurs only with a specific minimum or maximum value and should be checked against the minimum or maximum as appropriate.
Class Math
Unlike some of the numeric methods of class StrictMath , all implementations of the equivalent functions of class Math are not defined to return the bit-for-bit same results. This relaxation permits better-performing implementations where strict reproducibility is not required.
By default many of the Math methods simply call the equivalent method in StrictMath for their implementation. Code generators are encouraged to use platform-specific native libraries or microprocessor instructions, where available, to provide higher-performance implementations of Math methods. Such higher-performance implementations still must conform to the specification for Math .
The quality of implementation specifications concern two properties, accuracy of the returned result and monotonicity of the method. Accuracy of the floating-point Math methods is measured in terms of ulps, units in the last place. For a given floating-point format, an ulp of a specific real number value is the distance between the two floating-point values bracketing that numerical value. When discussing the accuracy of a method as a whole rather than at a specific argument, the number of ulps cited is for the worst-case error at any argument. If a method always has an error less than 0.5 ulps, the method always returns the floating-point number nearest the exact result; such a method is correctly rounded. A correctly rounded method is generally the best a floating-point approximation can be; however, it is impractical for many floating-point methods to be correctly rounded. Instead, for the Math class, a larger error bound of 1 or 2 ulps is allowed for certain methods. Informally, with a 1 ulp error bound, when the exact result is a representable number, the exact result should be returned as the computed result; otherwise, either of the two floating-point values which bracket the exact result may be returned. For exact results large in magnitude, one of the endpoints of the bracket may be infinite. Besides accuracy at individual arguments, maintaining proper relations between the method at different arguments is also important. Therefore, most methods with more than 0.5 ulp errors are required to be semi-monotonic: whenever the mathematical function is non-decreasing, so is the floating-point approximation, likewise, whenever the mathematical function is non-increasing, so is the floating-point approximation. Not all approximations that have 1 ulp accuracy will automatically meet the monotonicity requirements.
The platform uses signed two’s complement integer arithmetic with int and long primitive types. The developer should choose the primitive type to ensure that arithmetic operations consistently produce correct results, which in some cases means the operations will not overflow the range of values of the computation. The best practice is to choose the primitive type and algorithm to avoid overflow. In cases where the size is int or long and overflow errors need to be detected, the methods whose names end with Exact throw an ArithmeticException when the results overflow.
Math abs java что это
Unlike some of the numeric methods of class StrictMath , all implementations of the equivalent functions of class Math are not defined to return the bit-for-bit same results. This relaxation permits better-performing implementations where strict reproducibility is not required.
By default many of the Math methods simply call the equivalent method in StrictMath for their implementation. Code generators are encouraged to use platform-specific native libraries or microprocessor instructions, where available, to provide higher-performance implementations of Math methods. Such higher-performance implementations still must conform to the specification for Math .
The quality of implementation specifications concern two properties, accuracy of the returned result and monotonicity of the method. Accuracy of the floating-point Math methods is measured in terms of ulps, units in the last place. For a given floating-point format, an ulp of a specific real number value is the distance between the two floating-point values bracketing that numerical value. When discussing the accuracy of a method as a whole rather than at a specific argument, the number of ulps cited is for the worst-case error at any argument. If a method always has an error less than 0.5 ulps, the method always returns the floating-point number nearest the exact result; such a method is correctly rounded. A correctly rounded method is generally the best a floating-point approximation can be; however, it is impractical for many floating-point methods to be correctly rounded. Instead, for the Math class, a larger error bound of 1 or 2 ulps is allowed for certain methods. Informally, with a 1 ulp error bound, when the exact result is a representable number, the exact result should be returned as the computed result; otherwise, either of the two floating-point values which bracket the exact result may be returned. For exact results large in magnitude, one of the endpoints of the bracket may be infinite. Besides accuracy at individual arguments, maintaining proper relations between the method at different arguments is also important. Therefore, most methods with more than 0.5 ulp errors are required to be semi-monotonic: whenever the mathematical function is non-decreasing, so is the floating-point approximation, likewise, whenever the mathematical function is non-increasing, so is the floating-point approximation. Not all approximations that have 1 ulp accuracy will automatically meet the monotonicity requirements.
The platform uses signed two’s complement integer arithmetic with int and long primitive types. The developer should choose the primitive type to ensure that arithmetic operations consistently produce correct results, which in some cases means the operations will not overflow the range of values of the computation. The best practice is to choose the primitive type and algorithm to avoid overflow. In cases where the size is int or long and overflow errors need to be detected, the methods addExact , subtractExact , multiplyExact , and toIntExact throw an ArithmeticException when the results overflow. For other arithmetic operations such as divide, absolute value, increment by one, decrement by one, and negation, overflow occurs only with a specific minimum or maximum value and should be checked against the minimum or maximum as appropriate.
Numbers And Statics — Headfirst Java Chapter 10
The aim of the article is to highlight the key concepts discussed in Chapter 10.
Methods in the Math class don’t use any instance variable values. And because the methods are ‘static’, you don’t need to have an instance of Math. All you need is the Math class.
If you try to make an instance of class Math
Math mathObject = new Math();
You’ll get this error:
The difference between regular (non-static) and static methods.
Java is object-oriented, but once in a while you have a special case, typically a utility method (like the Math methods), where there is no need to have an instance of the class. The keyword static lets a method run without any instance of the class. A static method means “behavior not dependent on an instance variable, so no instance/object is required. Just the class.”
Call a static method using a class name:
Call a non-static method using a reference variable name
Static Methods Cannot Use Non-Static (Instance) Variables
Static methods run without knowing about any particular instance of the static method’s class. And as you saw on the previous pages, there might not even be any instances of that class. Since a static method is called using the class (Math. random()) as opposed to an instance reference (t2.play()), a static method can’t refer to any instance variables of the class. The static method doesn’t know which instance’s variable value to use.
Let’s look at an example:
if we run the Cat.java class we will get the below error.
Static Methods Can’t Use Non-Static Methods, Either
What non-static methods do is, usually use instance variable states to affect the behaviour of the method. A getName() method returns the value of the name variable. The object used to invoke the getName() method.
The below program also won’t compile.
<script src=”https://gist.github.com/BhagyaDevduni/804777216f0aac3c367718d64177fa88.js"></script>
Static Variable
Static variables are shared. All instances of the same class share a single copy of the static variables.
Static Variable
Static variables are shared. All instances of the same class share a single copy of the static variables.
Initializing a Static Variable
When the class is loaded, static variables are initialized. If we don’t explicitly initialize a static variable (by assigning it a value at the time we declare it), it gets a default value, Int variables are initialized to zero, which mean we didn’t need to explicitly say “playerCount = 0”. Declaring, but not initializing, a static variable means the static variable will get the default value for that variable type, in exactly the same way that instance variables are given default values when declared.
There are two guarantees about static variables.
1. Static variables in a class are initialized before any object of that class can be created
2. Static variables in a class are initialized before any static method of the class runs.
Final Keyword
Static Final Variables
When a variable is declared as final, it cannot be changed after initialization. As long as the class is loaded, the static final variable’s value won’t change.
public static final double PI = 3.141592653589793;
The variable is marked as public so that any code can access it. The variable is marked static so that don’t need an instance of class Math. The variable is marked final because PI doesn’t change.
There is a naming convention that makes it easier for you to identify a constant, but there is no other way to mark a variable as a constant. Constant variable names should be in all caps.
A static initializer is a block of code that runs when a class is loaded, before any other code can use the class, so it’s a great place to initialize a static final variable.
We can use the keyword final to modify non-static variables also, including instance variables, local variables, and method parameters.
Math methods
The Java Math class has many methods that allows you to perform mathematical tasks on numbers.
- Math.random()
Math.random() returns a random number between 0.0 (inclusive), and 1.0 (exclusive)
2. Math.abs()
Math.abs() method returns a double that is the absolute value of the argument. The method is overloaded, so if you pass it an int it returns an int. Pass it a double it returns a double.
3. Math.round()
It returns an int or a long (depending on whether the argument is a float or a double) rounded to the nearest integer value.
4. Math.min()
Math.min() method returns a value that is the minimum of the two arguments. The method is overloaded to take ints, longs, floats, or doubles.
5. Math.max()
Returns a value that is the maximum of the two arguments. The method is overloaded to take ints, longs, floats, or doubles.
*Wrapping a Primitive
When we want to treat primitives like an object, then we can do it by wrapping them. There’s a wrapper class for every primitive type, and since the wrapper classes are in java.lang package and we don’t need to import them. And also we can identify wrapper classes because, each one is named after the primitive type it wraps, but with the first letter capitalized to follow the class naming convention.
Math methods
The Java Math class has many methods that allows you to perform mathematical tasks on numbers.
- Math.random()
Math.random() returns a random number between 0.0 (inclusive), and 1.0 (exclusive)
2. Math.abs()
Math.abs() method returns a double that is the absolute value of the argument. The method is overloaded, so if you pass it an int it returns an int. Pass it a double it returns a double.
3. Math.round()
It returns an int or a long (depending on whether the argument is a float or a double) rounded to the nearest integer value.
4. Math.min()
Math.min() method returns a value that is the minimum of the two arguments. The method is overloaded to take ints, longs, floats, or doubles.
5. Math.max()
Returns a value that is the maximum of the two arguments. The method is overloaded to take ints, longs, floats, or doubles.
*Wrapping a Primitive
When we want to treat primitives like an object, then we can do it by wrapping them. There’s a wrapper class for every primitive type, and since the wrapper classes are in java.lang package and we don’t need to import them. And also we can identify wrapper classes because, each one is named after the primitive type it wraps, but with the first letter capitalized to follow the class naming convention.
Formatting consists of two main parts,
- Formatting instructions : Use special format specifiers that describe how the argument should be formatted
- The argument to be formatted : The argument type should be that can formatted. if you use double value in the argument there is a compilation error.
What do these instructions actually say is, “Take the second argument to this method, and format it as a decimal integer and insert commas.”
·format() → method is called the format string.
·The first argument to a format() method is called the format String, and it can include characters that we want printed as-is, without extra formatting.
·When we see the percent sign (%) think of it as representing a variable, and the variable is the other argument to the method. The rest of the characters after the percent sign describe the formatting instructions for the argument.
We can’t put anything after %
· %,d →insert commas and format the number as a decimal integer
· %.2f →format numbers as floating-point with a precision of to decimal places.
· %,2f →insert commas and format numbers as floating-point with a precision of to decimal places.
The format specifier
The Type is mandatory everything else is optional.
· % d →decimal
The Type is mandatory everything else is optional.
· % d →decimal
The argument must be compatible with an int, so that means only byte, short, int, and char (or their wrapper types)
· %f →floating-point
The argument must be of a floating point type, so that means only a float or double (primitive or wrapper) as well as something called Big Decimal.
· %x →hexadecimal
The argument must be a byte, short, int, or long. this can be including both primitives and wrapper types and also BigIntegers.
· %c →Character
The number 42 represents the char *. The argument must be a byte, short, int, or char. This can be including both primitives and wrapper types
*Formatting Date
The main difference between number and date formatting is that date formats use a two-character type that starts with “t”.
·The complete date and time represents % tc
·Just the time represents %tr
·Day of the week, month and day represents %tA %tB %td
There isn’t a single format specifier that will do exactly what we want, so we have to combine three of them for day of the week (%tA), month (%tB), and day of the month (%td).
*Getting An Object That Extends Calendar
Calendar cal = new Calendar(); is will not work .
Instead, use the static “getInstance()” method:
*Bullet Points
· A static method should be called using the class name rather than an object reference variable: Math. random() vs. myFoo.go()
· A static method can be invoked without any instances of the method’s class on the heap.
· A static method is good for a utility method that does not (and will never) depend on a particular instance variable value.
· A static method is not associated with a particular instance — only the class — so it cannot access any instance variable values of its class. It wouldn’t know which instance’s values to use.
· A static method cannot access a non-static method, since non-static methods are usually associated with an instance variable state.
· If you have a class with only static methods, and you do not want the class to be instantiated, you can mark the constructor private.
· A static variable is a variable shared by all members of a given class. There is only one copy of a static variable in a class, rather than one copy per each instance for instance variables.
· A static method can access a static variable.
· To make a constant in Java, mark a variable as both static and final.
· A final static variable must be assigned a value either at the time it is declared or in a static initializer.
· The naming convention for constants (final static variables) is to make the name all uppercase.
· A final variable value cannot be changed once it has been assigned.
· Assigning a value to a final instance variable must be either at the time it is declared or in the constructor.