groovy.lang.Binding difference between property and variable

Question

Couldn't really figure out/find what a difference between thouse two

import groovy.lang.Binding;
import groovy.lang.GroovyShell;

class Scratch {
    public static void main(String[] args) {
        Binding binding = new Binding();
        Integer p = 1,
                v = 1;
        binding.setProperty("p", p);
        binding.setVariable("v", v);

        GroovyShell shell = new GroovyShell(binding);
        shell.evaluate("p++;v++;");
        System.out.println(String.format("BINDING Property = %s, Variable = %s", binding.getProperty("p"), binding.getVariable("v")));
        System.out.println(String.format("JAVA Property = %s, Variable = %s", p, v));
    }
}

Output is:

BINDING Property = 2, Variable = 2
JAVA Property = 1, Variable = 1

Is there is some purpose for using one or another.

Answer 1

类groovy.lang.Binding重载setProperty和getProperty方法，以便您可以使用字段访问器或下标运算符访问变量。如果你看一下这两个方法的源代码，你会发现类似这样的内容：

/**
 * Overloaded to make variables appear as bean properties or via the subscript operator
 */
public Object getProperty(String property) {
    /** @todo we should check if we have the property with the metaClass instead of try/catch  */
    try {
        return super.getProperty(property);
    }
    catch (MissingPropertyException e) {
        return getVariable(property);
    }
}

/**
 * Overloaded to make variables appear as bean properties or via the subscript operator
 */
public void setProperty(String property, Object newValue) {
    /** @todo we should check if we have the property with the metaClass instead of try/catch  */
    try {
        super.setProperty(property, newValue);
    }
    catch (MissingPropertyException e) {
        setVariable(property, newValue);
    }
}

这意味着在 Groovy 中你可以表达

/**
 * Overloaded to make variables appear as bean properties or via the subscript operator
 */
public Object getProperty(String property) {
    /** @todo we should check if we have the property with the metaClass instead of try/catch  */
    try {
        return super.getProperty(property);
    }
    catch (MissingPropertyException e) {
        return getVariable(property);
    }
}

/**
 * Overloaded to make variables appear as bean properties or via the subscript operator
 */
public void setProperty(String property, Object newValue) {
    /** @todo we should check if we have the property with the metaClass instead of try/catch  */
    try {
        super.setProperty(property, newValue);
    }
    catch (MissingPropertyException e) {
        setVariable(property, newValue);
    }
}

作为

binding.setVariable("v", v);

当然，如果您正在访问的属性setProperty或getProperty类中存在该属性，那么您将无法使用该名称设置变量，在这种情况下，您需要调用binding.setVariable()直接调用。

另一方面，方法getVariable和setVariable直接读取或将值放入内部映射。它的源代码如下：

binding.v = v
// or
binding['v'] = v