Java重写类的HashCode

╰半夏微凉° 2022-05-24 14:05 138阅读 0赞

我们知道，每次创建一个对象，都会生成 一个新的HashCode，但是在某种情况下，我们希望同一个类的对象的HashCode相同，可以在类的下面写上如下代码即可：

@Override
    	public int hashCode() {
    		final int prime = 31;
    		int result = 1;
    		result = prime * result + ((id == null) ? 0 : id.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;
    		Products other = (Products) obj;
    		if (id == null) {
    			if (other.id != null)
    				return false;
    		} else if (!id.equals(other.id))
    			return false;
    		return true;
    	}

举一个例子：

package com.aynu.bookstore.beans;
    
    import java.io.Serializable;
    
    public class Products implements Serializable{
        private String id;
    
        private String name;
    
        private Double price;
    
        private String category;
    
        private Integer pnum;
    
        private String imgurl;
    
        private String description;
    
    	public String getId() {
    		return id;
    	}
    
    	public void setId(String id) {
    		this.id = id;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	public Double getPrice() {
    		return price;
    	}
    
    	public void setPrice(Double price) {
    		this.price = price;
    	}
    
    	public String getCategory() {
    		return category;
    	}
    
    	public void setCategory(String category) {
    		this.category = category;
    	}
    
    	public Integer getPnum() {
    		return pnum;
    	}
    
    	public void setPnum(Integer pnum) {
    		this.pnum = pnum;
    	}
    
    	public String getImgurl() {
    		return imgurl;
    	}
    
    	public void setImgurl(String imgurl) {
    		this.imgurl = imgurl;
    	}
    
    	public String getDescription() {
    		return description;
    	}
    
    	public void setDescription(String description) {
    		this.description = description;
    	}
    
    	public Products(String id, String name, Double price, String category, Integer pnum, String imgurl,
    			String description) {
    		super();
    		this.id = id;
    		this.name = name;
    		this.price = price;
    		this.category = category;
    		this.pnum = pnum;
    		this.imgurl = imgurl;
    		this.description = description;
    	}
    
    	public Products() {
    		super();
    		// TODO Auto-generated constructor stub
    	}
    
    	@Override
    	public String toString() {
    		return "Products [id=" + id + ", name=" + name + ", price=" + price + ", category=" + category + ", pnum="
    				+ pnum + ", imgurl=" + imgurl + ", description=" + description + "]";
    	}
    
    	@Override
    	public int hashCode() {
    		final int prime = 31;
    		int result = 1;
    		result = prime * result + ((id == null) ? 0 : id.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;
    		Products other = (Products) obj;
    		if (id == null) {
    			if (other.id != null)
    				return false;
    		} else if (!id.equals(other.id))
    			return false;
    		return true;
    	}
    }