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 stub

		ArrayList<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>
{

	@Override
	public int compare(String o1, String o2) {
		// TODO Auto-generated method stub
		int 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 stub
		TreeSet<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>
{

	@Override
	public int compare(String o1, String o2) {
		// TODO Auto-generated method stub
		int 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 stub

		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]
	}

}

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]