ValueRef (Spring Framework 4.3.30.RELEASE API)

所有已知实现类:
ValueRef.NullValueRef, ValueRef.TypedValueHolderValueRef
```
public interface ValueRef
```
Represents a reference to a value. With a reference it is possible to get or set the value. Passing around value references rather than the values themselves can avoid incorrect duplication of operand evaluation. For example in 'list[index++]++' without a value reference for 'list[index++]' it would be necessary to evaluate list[index++] twice (once to get the value, once to determine where the value goes) and that would double increment index.
从以下版本开始:
3.2
作者:
Andy Clement

嵌套类概要

嵌套类
修饰符和类型	接口	说明
`static class`	`ValueRef.NullValueRef`	A ValueRef for the null value.
`static class`	`ValueRef.TypedValueHolderValueRef`	A ValueRef holder for a single value, which cannot be set.

方法概要

所有方法实例方法抽象方法
修饰符和类型	方法	说明
`TypedValue`	`getValue()`	Returns the value this ValueRef points to, it should not require expression component re-evaluation.
`boolean`	`isWritable()`	Indicates whether calling setValue(Object) is supported.
`void`	`setValue(Object newValue)`	Sets the value this ValueRef points to, it should not require expression component re-evaluation.

- 方法详细资料
  - getValue
```
TypedValue getValue()
```
    Returns the value this ValueRef points to, it should not require expression component re-evaluation.
    返回:
    the value
  - setValue
```
void setValue(Object newValue)
```
    Sets the value this ValueRef points to, it should not require expression component re-evaluation.
    参数:
    newValue - the new value
  - isWritable
```
boolean isWritable()
```
    Indicates whether calling setValue(Object) is supported.
    返回:
    true if setValue() is supported for this value reference.