javase第十九講：Collections

學習了Comparator，接着看Collection

先看一個問題正序輸出幾個字母

package iterator;

import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;

/**
 * @Auther: Xinbai
 * @Date:2020/5/19 20:39
 */
public class TreeSetTest3 {
    public static void main(String[] args) {
        TreeSet set = new TreeSet();
        set.add("C");
        set.add("A");
        set.add("B");
        set.add("E");
        set.add("F");
        set.add("D");

        for (Iterator iter = set.iterator(); iter.hasNext(); ) {
            String value = (String)iter.next();
            System.out.println(value);
        }
    }
}

那麼反序？

package iterator;

import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;

/**
 * @Auther: Xinbai
 * @Date:2020/5/19 20:39
 */
public class TreeSetTest3 {
    public static void main(String[] args) {
        TreeSet set = new TreeSet(new Tess());
        set.add("C");
        set.add("A");
        set.add("B");
        set.add("E");
        set.add("F");
        set.add("D");

        for (Iterator iter = set.iterator(); iter.hasNext(); ) {
            String value = (String)iter.next();
            System.out.println(value);
        }
    }
}
class Tess implements Comparator{

    @Override
    public int compare(Object o1, Object o2) {
        String s1=(String)o1;
        String s2=(String)o2;
        return s2.compareTo(s1);
    }
}

package Collections;

import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedList;

/**
 * @Auther: Xinbai
 * @Date:2020/5/21 8:49
 */
public class CollectionsTest {
    public static void main(String[] args) {
        LinkedList list=new LinkedList();
        list.add(new Integer(-8));
        list.add(new Integer(20));
        list.add(new Integer(-20));
        list.add(new Integer(8));
        Comparator r= Collections.reverseOrder();
        Collections.sort(list,r);

        for (Iterator iter=list.iterator(); iter.hasNext();){
            System.out.println(iter.next());
        }
    }

那麼我們再看Collections的一個屬性shuffle【這個屬性使得數是隨機出現，也是搗亂順序】

  Collections.shuffle(list);
        for (Iterator iter=list.iterator(); iter.hasNext();){
            System.out.println(iter.next());
        }

最小值和最大值：

System.out.println(Collections.min(list));
        System.out.println(Collections.max(list));

輸出結果：
-20
20