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This article mainly introduces "the instance usage of Comparator class in Java". In the daily operation, I believe that many people have doubts about the instance usage of Comparator class in Java. The editor has consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about "the instance usage of Comparator class in Java". Next, please follow the editor to study!

Method 1: natural sorting: java. Lang. Comparable

> the Comparable interface forces the overall sorting of the objects of each class that implements it. This sort is called the natural sort of a class.

> the class that implements Comparable must implement the compareTo (Object obj) method. The two objects are compared through the return values of the compareTo (Object obj) method. Returns a positive integer if the current object this is greater than the formal parameter object obj, a negative integer if the current object this is less than the formal parameter object obj, and zero if the current object this is equal to the formal parameter pair obj.

> the list of objects (and arrays) that implement the Comparable interface can be done through Collections. Sort or Arrays. Sort performs automatic sorting. Objects that implement this interface can be used as keys in ordered maps or elements in ordered collections without specifying a comparator.

> for every E1 and e2 of class C, the natural ordering of class C is called consistent with equals if and only if e1.compareTo (e2) = = 0 and e1.equals (e2) have the same boolean value. It is recommended (though not necessary) to make the natural ordering consistent with equals.

/ * example of using Comparable API: natural sort 1. Such as String, wrapper class, etc., implement the Compareable interface, rewrite the compareTo (obj) method, and give a way to compare the size of the two objects. After overriding the compareTo () method, such as String and wrapper classes, they arrange 3. 5 from small to large. Rewrite the rule of compareTo (obj): if the current object this is greater than the formal parameter object obj, a positive integer is returned. If the current object this is less than the formal parameter object obj, a negative integer is returned. If the current object this is equal to the formal parameter object obj, then zero 4. For custom classes, if sorting is needed, we can have the custom class implement the Comparable interface and override the compareTo (obj) method to specify in the compareTo (obj) method how to sort * / @ Test public void test1 () {String [] arr = new String [] {"AA", "CC", "KK", "MM", "GG", "JJ", "DD"}; Arrays.sort (arr) System.out.println (Arrays.toString (arr)); / [AA, CC, DD, GG, JJ, KK, MM]} @ Test public void test2 () {Goods [] arr = new Goods [5]; arr [0] = new Goods ("lenovoMouse", 34); arr [1] = new Goods ("dellMouse", 43); arr [2] = new Goods ("miMouse", 12) Arr [3] = new Goods ("huaweiMouse", 65); arr [4] = new Goods ("microsoftMouse", 43); Arrays.sort (arr); System.out.println (Arrays.toString (arr)); method 2: custom sorting: java. Util. Comparator

> when the type of the element does not implement java. Lang. Comparable interface, but it is not convenient to modify the code, or implement java. Lang. The collation of the Comparable interface is not suitable for the current operation, so you can consider sorting objects using Comparator to force a comparison of the overall sorting of multiple objects.

> override the compare (Object o1, Object O2) method to compare the size of o1 and O2: if the method returns a positive integer, it means that o1 is greater than O2; if 0 is returned, it is equal; and a negative integer is returned, which means o1 is less than O2.

> you can pass Comparator to sort methods, such as Collections. Sort or Arrays. Sort), thus allowing precise control of the sort order.

You can also use Comparator to control the order of certain data structures, such as ordered set or ordered mapping, or to provide sorting for objects that do not have a natural order, colection.

/ * use of Comparator API: custom sort 1. Background: when the type of the element does not implement the java.long.Comparable interface and it is not convenient to modify the code, or the collation of the java.long.Comparable interface is not suitable for the current operation, then consider using Comparator objects to sort 2. Override the compare (Object o1 MagneObject O2) method to compare the size of o1 and O2: if the method returns an integer, it means that o1 is greater than O2. If 0 is returned, it is equal; a negative integer is returned, indicating that o1 is less than O2. * / @ Test public void test3 () {String [] arr = new String [] {"AA", "CC", "KK", "MM", "GG", "JJ", "DD"} Arrays.sort (arr,new Comparator () {/ / arranges @ Override public int compare (Object o1, Object O2) {if (o1 instanceof String & & O2 instanceof String) {String S1 = (String) o1; String S2 = (String) O2 Return-s1.compareTo (S2); / / add-means: arrange from small to big-> from big to small} throw new RuntimeException ("data types entered are inconsistent!") ;}}); System.out.println (Arrays.toString (arr)); / / [MM, KK, JJ, GG, DD, CC, AA] @ Test public void test4 () {Goods [] arr = new Goods [5]; arr [0] = new Goods ("lenovoMouse", 34); arr [1] = new Goods ("dellMouse", 43) Arr [2] = new Goods ("miMouse", 12); arr [3] = new Goods ("huaweiMouse", 65); arr [4] = new Goods ("microsoftMouse", 43) Arrays.sort (arr, new Comparator () {/ / indicate the size of goods: sort by product name from lowest to highest, and then sort by price from high to low @ Override public int compare (Object o1, Object o2) {if (o1 instanceof Goods & & O2 instanceof Goods) {Goods G1 = (Goods) o1 Goods G2 = (Goods) O2; if (g1.getName (). Equals (g2.getName () {return-Double.compare (g1.getPrice (), g2.getPrice ());} else {return g1.getName () .compareTo (g2.getName ()) }} throw new RuntimeException ("inconsistent data types entered!") ); System.out.println (Arrays.toString (arr));}

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