Comparator接口的使用方法

本文用一個小例子來闡述Comparator接口的使用方法。

主要是兩個JAVA檔案。

SortUtils.java: 實作接口、以及具體使用的例子

import java.util.Collections;
import java.util.Comparator;
import java.util.List;


public class SortUtils {
	enum SortType {
		SORT_TYPE_CASE_SENSITIVE,
		SORT_TYPE_CASE_INSENSITIVE
	};
	
	private static Comparator<String> caseSensitiveComparator = 
			new Comparator<String> () {

				public int compare(String s1, String s2) {
					return s1.compareTo(s2);
				}
			};
			
	private static Comparator<String> caseInsensitiveComparator = 
			new Comparator<String>() {

				public int compare(String s1, String s2) {
					return s1.compareToIgnoreCase(s2);
				}
	};
	
	public static void sort(List<String> values, SortType sortType) {
		switch (sortType) {
		case SORT_TYPE_CASE_SENSITIVE:
			Collections.sort(values, caseSensitiveComparator);
			return;
			
		case SORT_TYPE_CASE_INSENSITIVE:
			Collections.sort(values, caseInsensitiveComparator);
			return;
		
		default:
			// Unreachable here
			return;
		}
	}
}
           

SortTest.java: 對上述代碼進行驗證的代碼

import java.util.ArrayList;
import java.util.List;


public class SortTest {

	public static void main(String[] args) {
		List<String> values = new ArrayList<String>();
		values.add("first");
		values.add("second");
		values.add("third");
		values.add("FIRST");
		values.add("SECOND");
		values.add("THIRD");
		
		test("case sensitive", values, SortUtils.SortType.SORT_TYPE_CASE_SENSITIVE);
		test("case insensitive", values, SortUtils.SortType.SORT_TYPE_CASE_INSENSITIVE);

	}

	private static void test(String testcaseName, List<String> values, SortUtils.SortType sortType) {
		System.out.println(testcaseName);
		dump("    before: ", values);
		SortUtils.sort(values, sortType);
		dump("    after: ", values);
	}

	private static void dump(String title, List<String> values) {
		System.out.print(title);
		for (String s : values) {
			System.out.print(s);
			System.out.print(" ");
		}
		System.out.println();
	}

}
           

執行結果：

case sensitive
    before: first second third FIRST SECOND THIRD 
    after: FIRST SECOND THIRD first second third 
case insensitive
    before: FIRST SECOND THIRD first second third 
    after: FIRST first SECOND second THIRD third