toString()方法 一般出現在System.out.println(類名.toString());

toString()是一種自我描述方法 本身返回的是 getClass().getName() + "@" +Integer.toHexString(hashCode());

也就是類名 + @ +hashCode的值

重寫toString() 只會對類生效，并不能字符串生效; 例如

public class pratise {
    String num="aaaa";
    public String toString(){
        return num;
    }
   public static void main(String[] args){
       String s1="111";
       System.out.println(s1.toString());
       //輸出111 而并非aaaa;
   }
}

重寫toString()對類生效

package com.stu;
//用toString 重寫一個類
public class Car {	
   //成員變量
	private String carNo;
	private String carName;
	private String color;
	private double price;	
   //有參構造函數
	Car(String carNo,String carName,String color,double price){
		this.carNo=carNo;
		this.carName=carName;
		this.color=color;
		this.price=price;
	}	
	//get set方法
	public String getCarNo(){
		return carNo;
	}	
	public void setCarNo(String carNo){
		this.carNo=carNo;
	}	
	public String getCarName() {
		return carName;
	}
	public void setCarName(String carName) {
		this.carName = carName;
	}
	public String getColor() {
		return color;
	}
	public void setColor(String color) {
		this.color = color;
	}
	public double getPrice() {
		return price;
	}
	public void setPrice(double price) {
		this.price = price;
	}	
       //重寫toString();
	public String toString(){
		return "這個汽車名叫 "+carName+",型號是 "+carNo+",汽車顏色 "+color+",價格 "+price;
	}	
	public static void main(String[] args){
       //創建一個Car的對象
	Car myCar=new Car("蘇A 4995","長安汽車","灰藍色",70000.00);   //類名開頭字母大寫
        System.out.println(myCar.toString());
	}
}

輸出結果:

假如不對toString()進行重寫則 輸出結果:

 com.stu.Car@2542880d  ==> 類名 + “@” +hashCode值