Java 自 定 义 对 象 实 现 去 重

1.概述

set集合的特点是：set无序，不可以有重复元素
hashset：数据结构为哈希表，线程是非同步的。保证元素唯一性的原理是：判断元素的hashcode值是否相同，如果相同，还会继续判断元素的euals方法，是否为ture；为ture，则是同一个对象，否则不是。
treeset：可以对set集合元素进行排序，数据结构为二叉树。保证元素唯一性的原理是：compareTo方法返回0；

简单说：hashset去重（hashcode，equals），散列。treeset方法：去重（实现comparale或comparator接口重写自定义方法中，compareto方法返回0的条件是判断去重的依据），排序（实现comparale或comparator接口重写自定义方法中，compareto方法返回的+1，-1,0，进行排序）

2.使用treeset实现去重：1.自定义一个对象，2.定义一个容器，让其具有比较性（实现comparator接口，重写compare方法），将此对象作为参数传入 treeset中，

   public class Teacher {
private String name;
private int age;


/**  
* Creates a new instance of Teacher.  
*  
* @param name
* @param age  
*/  

public Teacher(String name, int age) {
super();
this.name = name;
this.age = age;
}


/**  
* name.  
*  
* @return  the name  
* @since   JDK 1.6  
*/
public String getName() {
return name;
}


/**  
* name.  
*  
* @param   name    the name to set  
* @since   JDK 1.6  
*/
public void setName(String name) {
this.name = name;
}


/**  
* age.  
*  
* @return  the age  
* @since   JDK 1.6  
*/
public int getAge() {
return age;
}


/**  
* age.  
*  
* @param   age    the age to set  
* @since   JDK 1.6  
*/
public void setAge(int age) {
this.age = age;
}


}



}
  public class MyCompare implements Comparator<Object> {
@Override
public int compare(Object o1, Object o2) {
 
// TODO Auto-generated method stub  
Teacher s1=(Teacher)o1;
Teacher s2=(Teacher)o2;
int n=s1.getName().compareTo(s2.getName());
if(n==0){//姓名相同，比较统计数
n=new Integer(s1.getAge()).compareTo(s2.getAge());
}
return n;
}
}
  测试类：

System.out.println("==================");
Set<Teacher> t=new TreeSet<Teacher>(new MyCompare());
t.add(new Teacher("liu",89));
t.add(new Teacher("jian",123));
t.add(new Teacher("jian",123));

t.add(new Teacher("juf",123));

t.add(new Teacher("four",4));
t.add(new Teacher("ni",56));
t.add(new Teacher("ni",56));
t.add(new Teacher("hao",23));
System.out.println("排序后遍历:");
for(Teacher s:t){
System.out.println(s.getName()+"=="+s.getAge());
}

结果为:

排序后遍历:

1.four==4
2.hao==23
3.jian==123 
4.juf==123  //
5.liu==89
6.ni==56
结论：结果的3,4说明：只有name，age同时相同才判断为同一对象。符合我们在自定义 的compare方法中定义的：姓名相同比较age，如果age比较后返回0，既是同一个对象，去重。

2.使用hashset实现去重：我们知道treeset，hashset存储的类型为string，interger等常用类型均能实现自动的去重。但如果要实现自定义对象实现去重效果，则需要自定义对象实现equals和hashcode方法。

2.1 以对象的所有属性相同作为重复的依据

public  class EntityTerm2  {
private String name;//名称
private String termNature;//词性
private String age;


public String getName() {
return name;
}


public void setName(String name) {
this.name = name;
}


public String getTermNature() {
return termNature;
}


public void setTermNature(String termNature) {
this.termNature = termNature;
}


public String getAge() {
return age;
}


public void setAge(String age) {
this.age = age;
}


@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((age == null) ? 0 : age.hashCode());
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result
+ ((termNature == null) ? 0 : termNature.hashCode());
return result;
}


@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
EntityTerm2 other = (EntityTerm2) obj;


if (age == null) {
if (other.age != null)
return false;
} else if (!age.equals(other.age))
return false;

if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;

if (termNature == null) {
if (other.termNature != null)
return false;
} else if (!termNature.equals(other.termNature))
return false;

return true;
}
 


public EntityTerm2(String name, String termNature, String age) {
super();
this.name = name;
this.termNature = termNature;
this.age = age;
}

}
  public class Test {
public static void main(String[] args){  

    Set<EntityTerm2> et2=new HashSet<EntityTerm2>();//
         et2.add(new EntityTerm2("zhangsan","nr","123"));
      et2.add(new EntityTerm2("zhangsan","nrd","1234"));
      et2.add(new EntityTerm2("lisi","ntc","45"));
      et2.add(new EntityTerm2("wanwu","nr","4"));
      for(EntityTerm2 e:et2){
     System.out.println(e.getName()+"!!!"+e.getAge());
      }
   }
}

结果为：

lisi!!!45
wanwu!!!4
zhangsan!!!1234
zhangsan!!!123

修改元素有相同值时：

  public class Test {
public static void main(String[] args){  


   Set<EntityTerm2> et2=new HashSet<EntityTerm2>();//使用treeset存放对象，对象必须实现comparable接口，hashset则不用
      et2.add(new EntityTerm2("zhangsan","nr","123"));
      et2.add(new EntityTerm2("zhangsan","nr","123"));
      et2.add(new EntityTerm2("lisi","ntc","45"));
      et2.add(new EntityTerm2("wanwu","nr","4"));
      for(EntityTerm2 e:et2){
     System.out.println(e.getName()+"!!!"+e.getAge());
      }
   }
}

结果为:

lisi!!!45
wanwu!!!4
zhangsan!!!123

1.2  以对象的name的值相同作为重复的依据

public  class EntityTerm2 implements Comparable<EntityTerm2> {
private String name;//名称
private String termNature;//词性
private String age;


public String getName() {
return name;
}


public void setName(String name) {
this.name = name;
}


public String getTermNature() {
return termNature;
}


public void setTermNature(String termNature) {
this.termNature = termNature;
}


public String getAge() {
return age;
}


public void setAge(String age) {
this.age = age;
}


@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}


public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
EntityTerm2 other = (EntityTerm2) obj;


if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;

return true;
}
 


public EntityTerm2(String name, String termNature, String age) {
super();
this.name = name;
this.termNature = termNature;
this.age = age;
}


}


public class Test {
public static void main(String[] args){  


    Set<EntityTerm2> et2=new HashSet<EntityTerm2>();//使用treeset存放对象，对象必须实现comparable接口
      et2.add(new EntityTerm2("zhangsan","nrd","123"));//hashset则不用，实现了去重
      et2.add(new EntityTerm2("zhangsan","nr2","123d"));
      et2.add(new EntityTerm2("lisi","ntc","45"));
      et2.add(new EntityTerm2("wanwu","nr","4"));
      for(EntityTerm2 e:et2){
     System.out.println(e.getName()+"!!!"+e.getAge());
      }
   }
}
结果为:
zhangsan!!!123
lisi!!!45
wanwu!!!4