JAVA中重写toString

最新推荐文章于 2024-10-03 10:00:00 发布

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本文介绍如何通过重写toString()方法来定制Java对象的显示形式，并提供了详细的代码示例。此外，还介绍了TreeSet集合的使用及自定义排序方法。

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]]