普通情况下在实现对对象元素的数组或集合进行排序的时候会用到Comparator和Comparable接口，通过在元素所在的类中实现这两个接口中的一个。然后对数组或集合调用Arrays.sort或者Collentions.sort方法就可以实现对数组或集合的排序。就sort方法里面的參数来说。实现了不同的接口则传递的參数也不尽同样。对于实现了Comparator接口的类来说。sort方法须要接受的參数不仅包含数组或集合。还要包含实现了该接口的类对象。而对实现了Comparable接口的类来说，參数不仅包含数组或者集合，还要包含实现了该接口的类对象。
详细怎么差别呢，事实上非常easy，由于看两个接口所实现的方法就知道，Comparator定义的方法为compare(Object o1, Object o2)。方法涉及两个类对象。所以须要在另外一个新的类来实现对数组元素的比較，所以在调用sort方法时须要传递这个额外的实现了Comparator接口的类对象；而实现了Comparable接口的类实在元素类的内部实现了排序的逻辑，所以调用sort方法时不须要传递额外的类对象。废话少说，直接上代码。
1.通过实现Comparator接口来实现对数组或集合的比較
class SortCat implements Comparator<Cat1>
{
@Override
public int compare(Cat1 o1, Cat1 o2)//实现了Comparator接口的compare方法
{
// TODO Auto-generated method stub
int size1=o1.getSize(),size2=o2.getSize();
if(size1!=size2)
return size1-size2;
return o1.getColor().compareTo(o2.getColor());
}
}
class Cat1
{
private String color;
private int size;
public Cat1(String color,int size)
{
this.color=color;
this.size=size;
}
public int getSize()
{
return size;
}
public String getColor()
{
return color;
}
public String toString()
{
return color+" cat,size = "+size;
}
}
public class HashMapComparatorDemo
{
public static void main(String[] args)
{
// TODO Auto-generated method stub
String colorArr[]={"black","yellow","white","colorful","gray","brown","blue","orange"};
int catSizeArr[]={5,3,7,9,6,4,1,8,2};
Random random=new Random();
Cat1 catArr[]=new Cat1[10];
int sizeIndex=0,colorIndex=0;
for(int i=0;i<10;i++)
{
sizeIndex=random.nextInt(catSizeArr.length);
colorIndex=random.nextInt(colorArr.length);
catArr[i]=new Cat1(colorArr[colorIndex], catSizeArr[sizeIndex]);
System.out.println("Color:"+catArr[i].getColor()+",size:"+catArr[i].getSize());
}
System.out.println("
After change the order....
");
Arrays.sort(catArr,new SortCat());//不仅要传递数组參数。还要传递实现了Comparator接口的类对象
for(Cat1 cat:catArr)
System.out.println("Color:"+cat.getColor()+",size:"+cat.getSize());
}
}结果：
Color:white,size:4
Color:colorful,size:4
Color:colorful,size:4
Color:gray,size:5
Color:yellow,size:7
Color:orange,size:6
Color:black,size:2
Color:colorful,size:8
Color:black,size:3
Color:yellow,size:2
After change the order....
Color:black,size:2
Color:yellow,size:2
Color:black,size:3
Color:colorful,size:4
Color:colorful,size:4
Color:white,size:4
Color:gray,size:5
Color:orange,size:6
Color:yellow,size:7
Color:colorful,size:82.通过实现Comparable接口来实现对数组或集合的比較
class Cat2 implements Comparable<Cat2>
{
private String color;
private int size;
public Cat2(String color,int size)
{
this.color=color;
this.size=size;
}
public int getSize()
{
return size;
}
public String getColor()
{
return color;
}
public String toString()
{
return color+" cat,size = "+size;
}
@Override
public int compareTo(Cat2 o)//在元素类里面实现comparable接口所定义的方法
{
// TODO Auto-generated method stub
int size=o.getSize();
if(this.size!=size)
return this.size-size;
return this.color.compareTo(o.getColor());
}
}
public class HashMapComparatorDemo2
{
public static void main(String[] args)
{
String colorArr[]={"black","yellow","white","colorful","gray","brown","blue","orange"};
int catSizeArr[]={5,3,7,9,6,4,1,8,2};
Random random=new Random();
Cat2 catArr[]=new Cat2[10];
int sizeIndex=0,colorIndex=0;
for(int i=0;i<10;i++)
{
sizeIndex=random.nextInt(catSizeArr.length);
colorIndex=random.nextInt(colorArr.length);
catArr[i]=new Cat2(colorArr[colorIndex], catSizeArr[sizeIndex]);
System.out.println("Color:"+catArr[i].getColor()+",size:"+catArr[i].getSize());
}
System.out.println("
After change the order....
");
Arrays.sort(catArr);//仅须要传递数组或集合就可以
for(Cat2 cat:catArr)
System.out.println("Color:"+cat.getColor()+",size:"+cat.getSize());
}
}结果：
Color:gray,size:7
Color:orange,size:9
Color:gray,size:3
Color:brown,size:5
Color:orange,size:1
Color:gray,size:8
Color:colorful,size:9
Color:white,size:1
Color:blue,size:7
Color:brown,size:1
After change the order....
Color:brown,size:1
Color:orange,size:1
Color:white,size:1
Color:gray,size:3
Color:brown,size:5
Color:blue,size:7
Color:gray,size:7
Color:gray,size:8
Color:colorful,size:9
Color:orange,size:93.另外。还能够用实现了对Comparable接口treeMap、treeSet进行排序，详细应用范围非常广。包含求一个无反复无序数组的前k项元素就能够用treeSet或treeMap非常好滴实现，循环建tree并维持一个大小为k的treeSet或treeMap就可以。超出范围的话先插入一个元素。然后删除排在最后的元素就可以。以下这段代码只实现的是有序建树并将treeMap输出出来的功能。
class Cat implements Comparable<Cat>
{
private String color;
private int size;
public Cat(String color,int size)
{
this.color=color;
this.size=size;
}
public int getSize()
{
return size;
}
public String getColor()
{
return color;
}
@Override
public int compareTo(Cat o)
{
// //优先依据颜色排序
// String color1=o.getColor();
// if(this.color.compareTo(color1)!=0)
// return this.color.compareTo(color1);
// return this.size-o.size;
//优先依据大小排序
int size=o.getSize();
if(this.size!=size)
return this.size-size;
return this.color.compareTo(o.getColor());
}
public String toString()
{
return "Color:"+color+",size = "+size;
}
}
public class HashMapComparableDemo
{
public static void main(String[] args)
{
SortedMap<Cat, Integer>map=new TreeMap();
String colorArr[]={"black","yellow","white","colorful","gray","brown","blue","orange"};
int catSizeArr[]={5,3,7,9,6,4,1,8,2};
Random random=new Random();
int sizeIndex=0,colorIndex=0,count=0;;
int mapSize=10;
for(int i=0;i<mapSize;i++)
{
sizeIndex=random.nextInt(catSizeArr.length);
colorIndex=random.nextInt(colorArr.length);
count=random.nextInt(20)+5;
map.put(new Cat(colorArr[colorIndex], catSizeArr[sizeIndex]), count);
}
Iterator<Entry<Cat, Integer>>iterator=map.entrySet().iterator();
Entry<Cat, Integer>entry;
while(iterator.hasNext())
{
entry=iterator.next();
System.out.println(entry.getKey().toString()+",Count:"+entry.getValue().toString());
}
}
}结果：
Color:black,size = 1,Count:15
Color:black,size = 2,Count:12
Color:gray,size = 2,Count:24
Color:brown,size = 5,Count:24
Color:gray,size = 5,Count:14
Color:brown,size = 6,Count:13
Color:white,size = 6,Count:7
Color:yellow,size = 6,Count:12
Color:gray,size = 7,Count:9
Color:brown,size = 8,Count:17另外：对某些对象建立treeMap或hashMap的时候还须要重写一下equals方法，防止发生插入同样元素的情况，由于默认情况下treeMap或HashMap是应该是以对象的引用作为各个对象元素的标志。而不是元素的值。