当需要将一个对象输出到显示器时,通常要调用他的toString()方法,将对象的内容转换为字符串.java中的所有类默认都有一个toString()方法
默认情况下 System.out.println(对象名)或者System.out.println(对象名.toString())输出的是此对象的类名和此对象对应内存的首地址 如果想自定义输出信息必须重写toString()方法
注意事项
1.必须被声明为public
2.返回类型为String
3.方法的名称必须为toString,且无参数
4.方法体中不要使用输出方法System.out.println()
import java.util.*;
public class TreeSetTest {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
SortedSet<Item> parts=new TreeSet<Item>();
parts.add(new Item("Toaster", 1234));
parts.add(new Item("Widget", 4562));
parts.add(new Item("Modem", 9912));
System.out.println(parts);
SortedSet<Item> sortByDescription=new TreeSet<Item>(new
Comparator<Item>()
{
public int compare(Item a, Item b)
{
String descrA=a.getDescription();
String descrB=b.getDescription();
return descrA.compareTo(descrB);
}
});
sortByDescription.addAll(parts);
System.out.println(sortByDescription);
}
}
class Item implements Comparable<Item>
{
public Item(String aDescription, int aPartNumber)
{
description=aDescription;
partNumber=aPartNumber;
}
public String getDescription()
{
return description;
}
public boolean equals(Object otherObject)
{
if(this==otherObject)
return true;
if(otherObject==null)
{
return false;
}
if (getClass()!=otherObject.getClass())
{
return false;
}
Item other=(Item)otherObject;
return description.equals(other.description)&&
partNumber==other.partNumber;
}
public int hashCode()
{
return 13*description.hashCode()+17*partNumber;
}
public int compareTo(Item other)
{
return partNumber-other.partNumber;
}
private String description;
private int partNumber;
}
输出为:
[Item@8c9e3a56, Item@d780c206, Item@39c021ba] [Item@39c021ba, Item@8c9e3a56, Item@d780c206]
Item重载toString()方法后：
import java.util.*;
public class TreeSetTest {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
SortedSet<Item> parts=new TreeSet<Item>();
parts.add(new Item("Toaster", 1234));
parts.add(new Item("Widget", 4562));
parts.add(new Item("Modem", 9912));
System.out.println(parts);
SortedSet<Item> sortByDescription=new TreeSet<Item>(new
Comparator<Item>()
{
public int compare(Item a, Item b)
{
String descrA=a.getDescription();
String descrB=b.getDescription();
return descrA.compareTo(descrB);
}
});
sortByDescription.addAll(parts);
System.out.println(sortByDescription);
}
}
class Item implements Comparable<Item>
{
public Item(String aDescription, int aPartNumber)
{
description=aDescription;
partNumber=aPartNumber;
}
public String getDescription()
{
return description;
}
public String toString()
{
return "[description="+description
+",partNumber="+partNumber+"]";
}
public boolean equals(Object otherObject)
{
if(this==otherObject)
return true;
if(otherObject==null)
{
return false;
}
if (getClass()!=otherObject.getClass())
{
return false;
}
Item other=(Item)otherObject;
return description.equals(other.description)&&
partNumber==other.partNumber;
}
public int hashCode()
{
return 13*description.hashCode()+17*partNumber;
}
public int compareTo(Item other)
{
return partNumber-other.partNumber;
}
private String description;
private int partNumber;
}
输出为:
[[description=Toaster,partNumber=1234], [description=Widget,partNumber=4562], [description=Modem,partNumber=9912]] [[description=Modem,partNumber=9912], [description=Toaster,partNumber=1234], [description=Widget,partNumber=4562]]
总结
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