java 中toString（）方法详解

1．toString（）方法

Object类具有一个toString()方法，你创建的每个类都会继承该方法。它返回对象的一个String表示，并且对于调试非常有帮助。然而对于默认的toString()方法往往不能满足需求，需要覆盖这个方法。

toString（）方法将对象转换为字符串。看以下代码：

package sample;

 

class Villain {

    private String name;

 

    protected void set(String nm) {

       name = nm;

    }

 

    public Villain(String name) {

       this.name = name;

    }

 

    public String toString() {

       return "I'm a Villain and my name is " + name;

    }

}

 

public class Orc extends Villain {

    private int orcNumber;

 

    public Orc(String name, int orcNumber) {

       super(name);

       this.orcNumber = orcNumber;

    }

 

    public void change(String name, int orcNumber) {

       set(name);

       this.orcNumber = orcNumber;

    }

 

    public String toString() {

       return "Orc" + orcNumber + ":" + super.toString();

    }

 

    public static void main(String[] args) {

       Orc orc = new Orc("Limburger", 12);

       System.out.println(orc);

       orc.change("Bob", 19);

       System.out.println(orc);

    }

}

 

结果：

sample.Orc@11b86e7

sample.Orc@11b86e7

如果去掉注释，即加入2个toString（）方法后，得到

结果：

Orc12:I'm a Villain and my name is Limburger

Orc19:I'm a Villain and my name is Bob

 

2．在容器类中使用toString()

编写一个工具类，用于在控制台输出Iterator。

import java.util.Iterator;

 

public class Printer {

    static void printAll(Iterator e){

       while(e.hasNext()){

           System.out.println(e.next());

       }

    }

}

在Hamster类中重写父类的toString（）方法。

public class Hamster {

    private int hamsterNumber;

    public Hamster(int hamsterNumber){

       this.hamsterNumber=hamsterNumber;

    }

 

    public String toString(){

       return "This is Hamster #"+hamsterNumber;

    }

}

在HamsterMaze类中使用容器类加载Hamster类对象并输出结果。

import java.util.ArrayList;

import java.util.List;

 

public class HamsterMaze {

    @SuppressWarnings("unchecked")

    public static void main(String[] args){

       List list=new ArrayList();

       for(int i=0;i<3;i++)

           list.add(new Hamster(i));

       Printer.printAll(list.iterator());

    }

}

结果：

This is Hamster #0

This is Hamster #1

This is Hamster #2

 

3．一个实现toString()的通用的Bean

在作一个项目时发现,许多bean需要实现toString()方法,就实现一个通用的bean,然后通过其他继承即可。

import java.lang.reflect.Field;

 

public class BaseBean {

  

    public String toString() {

       StringBuffer sb = new StringBuffer();

       try {

           Class t = this.getClass();

           Field[] fields = t.getDeclaredFields();

           for (int i = 0; i < fields.length; i++) {

              Field field = fields[i];

              field.setAccessible(true);

              sb.append("{");

              sb.append(field.getName());

              sb.append(":");

              if (field.getType() == Integer.class) {

                  sb.append(field.getInt(this));

              } else if (field.getType() == Long.class) {

                  sb.append(field.getLong(this));

              } else if (field.getType() == Boolean.class) {

                  sb.append(field.getBoolean(this));

              } else if (field.getType() == char.class) {

                  sb.append(field.getChar(this));

              } else if (field.getType() == Double.class) {

                  sb.append(field.getDouble(this));

              } else if (field.getType() == Float.class) {

                  sb.append(field.getFloat(this));

              } else

                  sb.append(field.get(this));

              sb.append("}");

           }

       } catch (Exception e) {

           e.printStackTrace();

       }

       return sb.toString();

    }

}

 

测试类

public class TestBean extends BaseBean {

 

    private int id;

 

    public int getId() {

       return id;

    }

 

    public void setId(int id) {

       this.id = id;

    }

 

    public static void main(String[] args) {

       TestBean testBean = new TestBean();

       testBean.setId(9);

       System.out.println(testBean.toString());

    }

}

结果

{id:9}