object | 易学教程

Passing null to the Overloaded methods [duplicate]

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问题 This question already has answers here : Method Overloading for null argument (7 answers) Closed 3 years ago . I am confused with the Output of the following two programs. When I'm only having two methods with parameters as String and Object in Program 1 it gives me output as String . But when I add a new method with parameter as Integer in Program 2 it won't compile and gives error as The method nullTest(Object) is ambiguous for the type testNull Program 1 : package onkartest; public class

In JavaScript is Object.keys().forEach() less memory efficient than a simple for…in loop?

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问题 Imagine you have a very large JS object, containing millions of key/value pairs, and you need to iterate over them. This jsPerf example shows the main ways to do it, and outlines the speed differences. What I wonder though is: using Object.keys() would have a different impact on memory compared to the other looping methods, since it needs to create the "index" array that contains all the object keys first? Are there any optimizations in the source code that prevent this? 回答1: What you're

vue 双向数据绑定原理

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博客地址： https://ainyi.com/8 采用defineProperty的两个方法get、set 示例 1  2 <input type="text" id="input"> 3  4 <p id="desc"></p> 1 let obj = {}; 2 let temp = {};//采用临时变量代理obj 3 Object.defineProperty(obj,'name',{ 4 //获取obj的name属性会触发 5 get(){ 6 return temp['name']; 7 }, 8 //给obj的name属性赋值会触发 9 set(val){ 10 temp['name'] = val;//改变temp的结果 11 input.value = val;//将值赋值到输入框 12 desc.innerText = val; //将值显示到输入框下面 13 //obj.name = val; //死循环，不能采取这种方式赋值，采用temp代理方式赋值和取值 14 } 15 }); 16 17 //设置了id值不需要document.getElementById() 18 //调用上面的set方法，设置初始值 19 obj.name = "message"; 20 //调用上面的get方法，获取属性值并放到输入框

Testing nested objects as undefined in Javascript [duplicate]

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问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: javascript test for existence of nested object key I'm attempting to construct an error message for a formset by testing if a certain object is not undefined , and if it's not undefined , then I end up populating it with that error message. The main problem is that I have to validate if each nested object is undefined , which results in some pretty ugly code. Here's the example: errorsForField: function

What should I use as a lock object of a synchronized statement in Java

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问题 Could anyone explain what is the difference between these examples? Example # 1. public class Main { private Object lock = new Object(); private MyClass myClass = new MyClass(); public void testMethod() { // TODO Auto-generated method stub synchronized (myClass) { // TODO: modify myClass variable } } } Example # 2. package com.test; public class Main { private MyClass myClass = new MyClass(); private Object lock = new Object(); public void testMethod() { // TODO Auto-generated method stub

Approaches to preserving object's attributes during extract/replace operations

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问题 Recently I encountered the following problem in my R code. In a function, accepting a data frame as an argument, I needed to add (or replace, if it exists) a column with data calculated based on values of the data frame's original column. I wrote the code, but the testing revealed that data frame extract/replace operations , which I've used, resulted in a loss of the object's special (user-defined) attributes . After realizing that and confirming that behavior by reading R documentation (http

clearTimeout() not working

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问题 In the following code the clearTimeout() function doesn't seem to clear the timer. Please note: I've stripped the code down a bit to show the relevent parts. Any ideas? var Gallery = { next: function() { // does stuff }, close: function() { Gallery.slideshow("off"); }, slideshow: function(sw) { if (sw == "off") {clearTimeout(timer);} var timer = setTimeout(function() {Gallery.next();Gallery.slideshow();}, 1000); }, }; FULL CODE: <!doctype html> <html> <head> <meta charset="utf-8"> <title

clearTimeout() not working

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Java: Can I convert List of Object to List of String[] and vice versa?

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问题 Is this possible without going through the list and casting the objects? I also need to convert List<Object> to List<T> (T = predefined Object) if it's possible? Edit: for clarification, I'm trying to use List<Object> as a return type of a class method that is widely used in my code. 回答1: No. This is simply not a valid conversion, because not all Object s are String[] . You could have determined this for yourself in 2 lines of code. Edit It sounds like you need to write the method more

Determining a PHP object's name

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问题 In Java (well, Android's version at least) all objects have a getClass() method which returns the object's class and you can then call getSimpleName() to get the human-readable name of the object. This is great for logging. I'd like to be able to do something similar in a PHP program I've been working on. Is there any way to find out what type of object "this" is? 回答1: return get_class($this); 回答2: I think this php.net man page may have the answers your looking for: http://php.net/manual/en