compareTo is a method of a class. I will explain both methods using Strings and a self-written “Student” class as examples. For example, converting an int to an Integer, a double to a Double, and so on.If the conversion goes the other way, this is called unboxing.. 二. Comparable
接口中的compareTo compareTo方法内必须做非空判断（规范问题），当然int类型就不用了。 注意事项： 1、模型必须实现Comparable接口 2、Collection.sort(list)会自动调用compareTo,如果没有这句，list是不会排序的，也不会调用compareTo方法 The compareTo() method of Java Boolean class compares the Boolean instance with the Boolean argument and returns … ... public int compareTo( NumberSubClass referenceName ) Parameters. I'm not looking for the obvious naive implementation, but was wondering if there's an elegant one-liner code to do that (without creating a new Long(value)).. Maybe something like this: This lets you keep your doubles in an array of primitives, and avoid autoboxing before calling an instance method. Double[] dist = new Double[centroids.size()]; 回答3: In java primitive types don't have any methods. using the operators <, <=, ==, =>, >.That does not work for objects. You compare Java primitives (int, long, double, etc.) Arrays.sort(array) This tutorial shows various examples of sorting an array using such methods, especially using the Comparable and Comparator interfaces. It returns 0 if a equals b, and it returns a positive int if a > b. The best treatment of the issues is in Horstmann's Core Java Vol 1. The compareTo() method is a method of Integer class under java.lang package.This method compares two integer objects numerically. [TODO: Add explanation and example] a.compareTo(b) N/A : Comparable interface. but if you want to use compareTo just create a Double array. The compareTo() method returns an int that is negative if a b. How to Compare Two Objects in Java? This tutorial helps you how to use the Arrays utility class to sort elements in an array.. You know, the java.util.Arrays class provides various methods for sorting elements of an array, as simple as:. It returns the result of the value 0 if Integer is equal to the argument Integer, a value less than 0 if Integer is less than the argument Integer and a value greater than 0 if Integer is greater than the argument Integer. Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes. Java Integer compareTo() method. In this post, we will see how to sort a List of objects using Comparable in Java. It is possible to compare Byte, Long, Integer, etc. In order to sort a collection of objects (using some property) in Java, we can use the java.lang.Comparable interface which imposes a natural ordering on the objects of each class that implements it. Compares values and returns an int which tells if the values compare less than, equal, or greater than. Java - compareTo() Method - The method compares the Number object that invoked the method to the argument. Here is the simplest example of autoboxing: For objects, you either use a compare or a compareTo method instead. We assume that compareTo() method has been added to the class. The compareTo() method of Integer class of java.lang package compares two Integer objects numerically and returns the value 0 if this Integer is equal to the argument Integer; a value less than 0 if this Integer is numerically less than the argument Integer; and a value greater than 0 if this Integer is numerically greater than the argument Integer (signed comparison). Here is an example involving Fraction objects. You have to encapsulate your int in an instance of the class java.lang.Integer 回答2: for primitive types do not use compareTo, use == instead. Working on a sorted list I came to a point I needed to implement a compareTo() function for primitive long values. Primitive data types aren't classes and have no methods you can call. Java Boolean compareTo() method.
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