集合框架的工具类----Collections

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/* *集合框架的工具类 *Collections */import java.util.ArrayList;import java.util.Collections;import java.util.Comparator;public class CollectionsDemo {public static void main(String[] args) {sortDemo();System.out.println();binarySearshDemo();}public static void binarySearshDemo(){ArrayList<String> list=new ArrayList<String>();list.add("asdas");list.add("rtr");list.add("hh");list.add("hh");list.add("aa");list.add("asdadcsdfs");list.add("ujuku");Collections.sort(list);sop(list);//必须要先排序，才能使用binarySearch方法int index=Collections.binarySearch(list, "rtrq");int index1=halfSearch(list,"rtrq");sop("index:"+index);sop("index1:"+index1);}//binarySearch方法的原理public static int halfSearch(ArrayList<String> list,String key){int max,min,mid;max=list.size()-1;min=0;while(min<=max){mid=(min+max)>>1; //  /2;String str=list.get(mid);int num=str.compareTo(key);if(num>0)max=mid-1;else if(num<0)min=mid+1;elsereturn mid;}return -min-1;}//比较器原理(如果元素自身不具备比较器，就要自定义一个比较器)public static int halfSearch2(ArrayList<String> list,String key,Comparator<String> cmp){int max,min,mid;max=list.size()-1;min=0;while(min<=max){mid=(min+max)>>1; //  /2;String str=list.get(mid);int num=cmp.compare(str,key);if(num>0)max=mid-1;else if(num<0)min=mid+1;elsereturn mid;}return -min-1;}public static void sortDemo(){ArrayList<String> list=new ArrayList<String>();list.add("asdas");list.add("rtr");list.add("hh");list.add("hh");list.add("aa");list.add("asdadcsdfs");list.add("ujuku");sop("排序前：");sop(list);Collections.sort(list);sop("自然排序的结果：");sop(list);//int index=halfSearch2(list,"aa",new StrLenComparator());Collections.sort(list,new StrLenComparator());sop("按照长度排序：");sop(list);//sop(index);String valuemax=Collections.max(list);sop("valuemax:"+valuemax);String lenmax=Collections.max(list,new StrLenComparator());sop("Lenmax:"+lenmax);}public static void sop(Object obj){System.out.println(obj);}}class StrLenComparator implements Comparator<String>{@Overridepublic int compare(String s1, String s2) {// TODO 自动生成的方法存根if(s1.length()>s2.length())return 1;if(s1.length()<s2.length())return -1;return s1.compareTo(s2);}}
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