Java Collections

作者: 一亩三分甜 | 来源:发表于2019-09-14 23:36 被阅读0次

集合框架的工具类:Collections。

Collections.sort(List<T> list)排序

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo {
    public static void main(String[] args) {
        sortDemo();
    }
    public static void sortDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("z");

        sop(list);
        Collections.sort(list);
        sop(list);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[abcd, aaa, z, kkkkk, qq, z]
[aaa, abcd, kkkkk, qq, z, z]

Collections.sort(List<T> list, Comparator<? super T> c)传入自定义比较器排序

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class CollectionsDemo0 {
    public static void main(String[] args) {
        sortDemo();
    }
    public static void sortDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("z");

        sop(list);
        Collections.sort(list,new StrLenComparator());
        sop(list);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
class StrLenComparator implements Comparator<String>
{
    public int compare(String s1,String s2)
    {
        int num = new Integer(s1.length()).compareTo(new Integer(s2.length()));
        if (num == 0)
            return s1.compareTo(s2);
        return num;
    }
}
//输出
[abcd, aaa, z, kkkkk, qq, z]
[z, z, qq, aaa, abcd, kkkkk]

max(Collection<? extends T> coll, Comparator<? super T> comp)获取最大值

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class CollectionsDemo1 {
    public static void main(String[] args) {
        maxDemo();
    }
    public static void maxDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");

        sop(list);
        String maxString = Collections.max(list,new StrLenComparator());
        sop("max="+maxString);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
class StrLenComparator0 implements Comparator<String>
{
    public int compare(String s1,String s2)
    {
        int num = new Integer(s1.length()).compareTo(new Integer(s2.length()));
        if (num == 0)
            return s1.compareTo(s2);
        return num;
    }
}
//输出
[abcd, aaa, z, kkkkk, qq, zz]
max=kkkkk

binarySearch(List<? extends Comparable<? super T>> list, T key)二分查找,若集合未排序或元素不存在则返回负数。返回值为-(插入点)-1。元素存在返回角标索引。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo2 {
    public static void main(String[] args) {
        binarySearchDemo();
    }
    public static void binarySearchDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        sop(list);
        int index = Collections.binarySearch(list,"aaa");
        sop("index="+index);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[abcd, aaa, z, kkkkk, qq, zz]
index=-1

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo2 {
    public static void main(String[] args) {
        binarySearchDemo();
    }
    public static void binarySearchDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        sop(list);
        int index = Collections.binarySearch(list,"ddddd");
        sop("index="+index);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[abcd, aaa, z, kkkkk, qq, zz]
index=-3

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo2 {
    public static void main(String[] args) {
        binarySearchDemo();
    }
    public static void binarySearchDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        Collections.sort(list);
        sop(list);
        int index = Collections.binarySearch(list,"aaa");
        sop("index="+index);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[aaa, abcd, kkkkk, qq, z, zz]
index=0

二分查找原理

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo2 {
    public static void main(String[] args) {
        binarySearchDemo();
    }
    public static void binarySearchDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        Collections.sort(list);
        sop(list);
//        int index = Collections.binarySearch(list,"aaa");
        int index = halfSearch(list,"ddddd");
        sop("index="+index);
    }
    public static int halfSearch(List<String>list,String key)
    {
        int max,min,mid;
        max = list.size()-1;
        min = 0;
        while (min<=max)
        {
            mid = (max+min)>>1;//相当于/2
            String str = list.get(mid);
            int num = str.compareTo(key);
            if (num>0)
                max = mid - 1;
            else if(num < 0)
                min = mid + 1;
            else
                return mid;
        }
        return - min -1;
    }

    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[aaa, abcd, kkkkk, qq, z, zz]
index=-3

Collections.sort(List<T> list, Comparator<? super T> c)传入比较器

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class CollectionsDemo2 {
    public static void main(String[] args) {
        binarySearchDemo();
    }
    public static void binarySearchDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        Collections.sort(list,new StrLenComparator1());
        sop(list);
        int index = Collections.binarySearch(list,"ddddd",new StrLenComparator1());
        sop("index="+index);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[z, qq, zz, aaa, abcd, kkkkk]
index=-6

传入比较器，修改二分查找的比较方式。不传默认是自然顺序。

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class CollectionsDemo2 {
    public static void main(String[] args) {
        binarySearchDemo();
    }
    public static void binarySearchDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        Collections.sort(list,new StrLenComparator1());
        sop(list);
        int index = halfSearch2(list,"ddddd",new StrLenComparator1());
        sop("index="+index);
    }
    public static int halfSearch2(List<String>list,String key,Comparator cmp)
    {
        int max,min,mid;
        max = list.size()-1;
        min = 0;
        while (min<=max)
        {
            mid = (max+min)>>1;//相当于/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;
            else
                return mid;
        }
        return - min -1;
    }

    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
class StrLenComparator1 implements Comparator<String>
{
    public int compare(String s1,String s2)
    {
        int num = new Integer(s1.length()).compareTo(new Integer(s2.length()));
        if (num == 0)
            return s1.compareTo(s2);
        return num;
    }
}
//输出
[z, qq, zz, aaa, abcd, kkkkk]
index=-6

fill(List<? super T> list, T obj)方法

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo3 {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        Collections.sort(list);
        sop(list);
        Collections.fill(list,"pp");
        sop(list);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[aaa, abcd, kkkkk, qq, z, zz]
[pp, pp, pp, pp, pp, pp]

替换集合中部分元素

import java.util.*;

public class CollectionsDemo3 {
    public static void main(String[] args) {
        fillDemoFromTo(0,2);
    }
    public static void fillDemoFromTo(int start,int end)
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        Collections.sort(list);
        sop(list);
        ListIterator<String> it = list.listIterator();
        while (it.hasNext())
        {
            String str = it.next();
            int ind = list.indexOf(str);
            if (ind >= start && ind <= end)
                list.set(ind,"pp");
        }
        sop(list);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[aaa, abcd, kkkkk, qq, z, zz]
[pp, pp, pp, qq, z, zz]

replaceAll(List<T> list, T oldVal, T newVal)

import java.util.*;

public class CollectionsDemo3 {
    public static void main(String[] args) {
          replaceAllDemo();
    }
    public static void replaceAllDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        Collections.sort(list);
        sop(list);
        Collections.replaceAll(list,"aaa","pp");
        sop(list);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[aaa, abcd, kkkkk, qq, z, zz]
[pp, abcd, kkkkk, qq, z, zz]

reverse(List<?> list)

import java.util.*;

public class CollectionsDemo3 {
    public static void main(String[] args) {
        reverseDemo();
    }
    public static void reverseDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");
        Collections.sort(list);
        sop(list);
        Collections.reverse(list);
        sop(list);
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[aaa, abcd, kkkkk, qq, z, zz]
[zz, z, qq, kkkkk, abcd, aaa]

reverseOrder()

import java.util.*;
public class CollectionsDemo3 {
    public static void main(String[] args) {
        orderDemo();
    }
    public static void orderDemo()
    {
        TreeSet<String> ts = new TreeSet<String>(Collections.reverseOrder());
        ts.add("abcde");
        ts.add("aaa");
        ts.add("kkk");
        ts.add("zz");
        ts.add("ccc");
        Iterator<String> it = ts.iterator();
        while (it.hasNext())
        {
            System.out.println(it.next());
        }
    }
}
//输出
zz
kkk
ccc
abcde
aaa

reverseOrder(Comparator<T> cmp)传入比较器返回比较器

import java.util.*;
class StrLenComparator2 implements Comparator<String>
{
    public int compare(String s1,String s2)
    {
        int num = new Integer(s1.length()).compareTo(new Integer(s2.length()));
        if (num == 0)
        {
            return s1.compareTo(s2);
        }
        return num;
    }
}
public class CollectionsDemo3 {
    public static void main(String[] args) {
          orderDemo0();
    }
    public static void orderDemo0()
    {
        TreeSet<String> ts = new TreeSet<String>(Collections.reverseOrder(new StrLenComparator2()));
        ts.add("abcde");
        ts.add("aaa");
        ts.add("kkk");
        ts.add("zz");
        ts.add("ccc");
        ts.add("b");
        Iterator<String> it = ts.iterator();
        while (it.hasNext())
        {
            System.out.println(it.next());
        }
    }
}

swap(List<?> list, int i, int j)交换对应角标位置上的元素

import java.util.*;
public class CollectionsDemo3 {
    public static void main(String[] args) {
        swapDemo();
    }
    public static void swapDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");

        sop(list);
        Collections.swap(list,1,2);
        sop(list);
    }
   public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[abcd, aaa, z, kkkkk, qq, zz]
[abcd, z, aaa, kkkkk, qq, zz]

shuffleDemo(List<?> list)将list按照随机顺序重新排列。

import java.util.*;
public class CollectionsDemo3 {
    public static void main(String[] args) {
        shuffleDemo();
    }
    public static void shuffleDemo()
    {
        List<String> list = new ArrayList<String>();
        list.add("abcd");
        list.add("aaa");
        list.add("z");
        list.add("kkkkk");
        list.add("qq");
        list.add("zz");

        sop(list);
        Collections.shuffle(list);
        sop(list);
    }
   public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}
//输出
[abcd, aaa, z, kkkkk, qq, zz]
[kkkkk, zz, abcd, z, qq, aaa]

Java Collections

集合框架的工具类:Collections。

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