版权声明：关注微信公众号：摸鱼科技资讯，联系我们 https://blog.csdn.net/qq_36949176/article/details/87938562
Collections
Collections:是集合框架的工具类
里面的方法都是静态的
例子：
比较器
package cn.itcast.p2.comparator;
import java.util.Comparator;
public class ComparatorByLength implements Comparator<String> {
@Override
public int compare(String o1, String o2) {
int temp = o1.length() - o2.length();
return temp==0?o1.compareTo(o2): temp;
}
}
代码示例
package cn.itcast.p2.toolclass.collections.demo;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.TreeSet;
import cn.itcast.p2.comparator.ComparatorByLength;
public class CollectionsDemo {
/**
* @param args
*/
public static void main(String[] args) {
demo_1();
}
public static void demo_1(){
List<String> list = new ArrayList<String>();
list.add("abcde");
list.add("cba");
list.add("aa");
list.add("zzz");
list.add("cba");
list.add("nbaa");
System.out.println(list);
//对list集合进行指定顺序的排序。
// Collections.sort(list);
// mySort(list);
// mySort(list,new ComparatorByLength());
Collections.sort(list,new ComparatorByLength());
System.out.println(list);
}
public static <T> void mySort(List<T> list,Comparator<? super T> comp){
for (int i = 0; i < list.size()-1; i++) {
for (int j = i+1; j < list.size(); j++) {
if(comp.compare(list.get(i), list.get(j))>0){
// T temp = list.get(i);
// list.set(i, list.get(j));
// list.set(j, temp);
Collections.swap(list, i, j);
}
}
}
}
public static <T extends Comparable<? super T>> void mySort(List<T> list){
for (int i = 0; i < list.size()-1; i++) {
for (int j = i+1; j < list.size(); j++) {
if(list.get(i).compareTo(list.get(j))>0){
// T temp = list.get(i);
// list.set(i, list.get(j));
// list.set(j, temp);
Collections.swap(list, i, j);
}
}
}
}