guava Objects的惯用用法以及实现

guava Objects的常用用法以及实现
Objects主要用来重写toString和HashCode方法。里面还有一个方法firstNonNull(T, T)返回两个值中不为null的一个如果都位null.抛出空指针异常。

上代码看用法：

import com.google.common.base.Objects;

public class ObjectsLearn {
	private Integer id;
	private String name;
	private String address;
	
	public ObjectsLearn(Integer id, String name, String address) {
		super();
		this.id = id;
		this.name = name;
		this.address = address;
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	@Override
	public String toString() {
		//return "ObjectsLearn [id=" + id + ", name=" + name + ", address=" + address + "]";
		return Objects.toStringHelper(this).omitNullValues().add("id", id).add("name", name).add("address", address).toString();
	}
	
	@Override
	public int hashCode() {
		return Objects.hashCode(id,name,address);
	}
	public static void main(String[] args) {
		ObjectsLearn learn = new ObjectsLearn(1, "test", "天上");
		System.out.println(learn);
	}
}

看了一下 Objects.toStringHelper(this).omitNullValues().add("id", id).add("name", name).add("address", address).toString()这一段代码的源码记录一下：
Objects这一段代码采用链表的结构实现：

 public static final class ToStringHelper {
    private final String className;
    private final ValueHolder holderHead = new ValueHolder();
    private ValueHolder holderTail = holderHead;
    private boolean omitNullValues = false;

定义了一个链表的头holderHead；

private ValueHolder addHolder() {
      ValueHolder valueHolder = new ValueHolder();
      holderTail = holderTail.next = valueHolder;
      return valueHolder;
    }
这一段代码指向下一个节点；

private ToStringHelper addHolder(String name, @Nullable Object value) {
      ValueHolder valueHolder = addHolder();
      valueHolder.value = value;
      valueHolder.name = checkNotNull(name);
      return this;
    }
这一段代码首先调用addHolder指向下一个节点，然后给下一个节点赋值。