工具类Collections的使用
import java.util.ArrayList;import java.util.Collections;import java.util.Comparator;public class CollectionsDemos {public static void main(String[] args) {// TODO Auto-generated method stubArrayList<String> al = new ArrayList<String>();//调用自定义方法向集合中添加元素addElements(al);//System.out.println(al);//[afgd, dfdf, cc, kkk, kkk]//调用方法对集合内的元素进行排序Collections.sort(al);System.out.println(al);//[afgd, cc, dfdf, kkk, kkk]//调用自定义比较器进行比较，，依据字符串的长度对其进行比较Collections.sort(al, new MyComparaLength());System.out.println(al);//[cc, kkk, kkk, afgd, dfdf]}private static void addElements(ArrayList<String> al) {// 向容器中添加元素al.add("afgd");al.add("dfdf");al.add("cc");al.add("kkk");al.add("kkk");}}//自定义一个比较器，以字符串的长度为标准进行比较 class MyComparaLength implements Comparator<String>{@Overridepublic int compare(String o1, String o2) {// TODO Auto-generated method stubint num = o1.length()-o2.length();if(num==0)return o1.compareTo(o2);return num;}}
运行程序：
//获取集合中最长的元素String max = Collections.max(al,new MyComparaLength());System.out.println("集合中最长的元素是："+max);
运行程序
TreeSet 集合的演示
import java.util.Collections;import java.util.Comparator;import java.util.TreeSet;public class CollectionsDemo2 {public static void main(String[] args) {// TODO Auto-generated method stubTreeSet<String> ts = new TreeSet<String>(Collections.reverseOrder());ts = new TreeSet<String>(Collections.reverseOrder(new MyComparaLength()));ts.add( "abc");ts.add( "hahaha");ts.add( "zzz");ts.add( "aa");ts.add( "cba");System.out.println(ts);//[hahaha, zzz, cba, abc, aa]}}class MyComparaLength implements Comparator<String>{@Overridepublic int compare(String o1, String o2) {// TODO Auto-generated method stubint num = o1.length()-o2.length();if(num==0)return o1.compareTo(o2);return num;}}运行程序：
ArrayList集合的演示
import java.util.ArrayList;import java.util.Collections;public class ArrayListDemos2 {public static void main(String[] args) {// TODO Auto-generated method stubArrayList<String> a = new ArrayList<String>();a.add( "abc");a.add( "hahaha");a.add( "zzz");a.add( "aa");a.add( "cba");System.out.println(a);//[abc, hahaha, zzz, aa, cba]Collections.replaceAll(a, "aa", "5555");System.out.println(a);//[abc, hahaha, zzz, 5555, cba]}}
运行程序：
ArrayList<String> a = new ArrayList<String>();a.add( "abc");a.add( "hahaha");a.add( "zzz");a.add( "aa");a.add( "cba");System.out.println(a);//[abc, hahaha, zzz, aa, cba]Collections.replaceAll(a, "aa", "5555");System.out.println(a);//[abc, hahaha, zzz, 5555, cba]//对集合中元素的位置进行随机置换Collections.shuffle(a);System.out.println(a);//[5555, cba, abc, hahaha, zzz]
不要惧怕黑暗，人间没有永恒的夜晚;不要担心严寒，
