例如，有两个列表
List<String> goods = new ArrayList<String>();
goods.add("Vegetables");
goods.add("Foods");
goods.add("Drinks");
List<String> foods = new ArrayList<String>();
foods.add("Beef");
foods.add("Chicken");
将食物插入货物到Foods的位置的最佳方法是什么，即将Food替换为foods以及goods的内容？
因此"use strict";
let assets = {
//Properties to help track the assets being loaded
toLoad: 0,
loaded: 0,
//File extensions for different types of assets
imageExtensions: ["png", "jpg", "gif"],
fontExtensions: ["ttf", "otf", "ttc", "woff"],
jsonExtensions: ["json"],
audioExtensions: ["mp3", "ogg", "wav", "webm"],
//The `load` method creates and loads all the assets. Use it like this:
//`assets.load(["images/anyImage.png", "fonts/anyFont.otf"]);`
load(sources) {
//The `load` method will return a Promise when everything has loaded
return new Promise(resolve => {
//The `loadHandler` counts the number of assets loaded, compares
//it to the total number of assets that need to be loaded, and
//resolves the Promise when everything has loaded
let loadHandler = () => {
this.loaded += 1;
console.log(this.loaded);
//Check whether everything has loaded
if (this.toLoad === this.loaded) {
//Reset `toLoad` and `loaded` to `0` so you can use them
//to load more assets later if you need to
this.toLoad = 0;
this.loaded = 0;
console.log("Assets finished loading");
//Resolve the promise
resolve();
}
};
//Display a console message to confirm that the assets are
//being loaded
console.log("Loading assets...");
//Find the number of files that need to be loaded
this.toLoad = sources.length;
//Loop through all the source filenames and find out how
//they should be interpreted
sources.forEach(source => {
//Find the file extension of the asset
let extension = source.split(".").pop();
//Load images that have file extensions that match
//the imageExtensions array
if (this.imageExtensions.indexOf(extension) !== -1) {
this.loadImage(source, loadHandler);
}
//Load fonts
else if (this.fontExtensions.indexOf(extension) !== -1) {
this.loadFont(source, loadHandler);
}
//Load JSON files
else if (this.jsonExtensions.indexOf(extension) !== -1) {
this.loadJson(source, loadHandler);
}
//Load audio files
else if (this.audioExtensions.indexOf(extension) !== -1) {
this.loadSound(source, loadHandler);
//Display a message if a file type isn't recognized
}
else {
console.log("File type not recognized: " + source);
}
});
});
},
loadImage(source, loadHandler) {
//Create a new image and call the `loadHandler` when the image
//file has loaded
let image = new Image();
image.addEventListener("load", loadHandler, false);
//Assign the image as a property of the `assets` object so
//you can access it like this: `assets["path/imageName.png"]`
this[source] = image;
//Set the image's `src` property to start loading the image
image.src = source;
},
loadFont(source, loadHandler) {
//Use the font's filename as the `fontFamily` name
let fontFamily = source.split("/").pop().split(".")[0];
//Append an `@afont-face` style rule to the head of the HTML document
let newStyle = document.createElement("style");
let fontFace
= "@font-face {font-family: '" + fontFamily + "'; src: url('" + source + "');}";
newStyle.appendChild(document.createTextNode(fontFace));
document.head.appendChild(newStyle);
//Tell the `loadHandler` we're loading a font
loadHandler();
},
loadJson(source, loadHandler) {
//Create a new `xhr` object and an object to store the file
let xhr = new XMLHttpRequest();
//Use xhr to load the JSON file
xhr.open("GET", source, true);
//Tell xhr that it's a text file
xhr.responseType = "text";
//Create an `onload` callback function that
//will handle the file loading
xhr.onload = event => {
//Check to make sure the file has loaded properly
if (xhr.status === 200) {
//Convert the JSON data file into an ordinary object
let file = JSON.parse(xhr.responseText);
//Get the filename
file.name = source;
//Assign the file as a property of the assets object so
//you can access it like this: `assets["file.json"]`
this[file.name] = file;
//Texture atlas support:
//If the JSON file has a `frames` property then
//it's in Texture Packer format
if (file.frames) {
//Create the tileset frames
this.createTilesetFrames(file, source, loadHandler);
} else {
//Alert the load handler that the file has loaded
loadHandler();
}
}
};
//Send the request to load the file
xhr.send();
},
createTilesetFrames(file, source, loadHandler) {
//Get the tileset image's file path
let baseUrl = source.replace(/[^\/]*$/, "");
//Use the `baseUrl` and `image` name property from the JSON
//file's `meta` object to construct the full image source path
let imageSource = baseUrl + file.meta.image;
//The image's load handler
let imageLoadHandler = () => {
//Assign the image as a property of the `assets` object so
//you can access it like this:
//`assets["images/imageName.png"]`
this[imageSource] = image;
//Loop through all the frames
Object.keys(file.frames).forEach(frame => {
//The `frame` object contains all the size and position
//data for each sub-image.
//Add the frame data to the asset object so that you
//can access it later like this: `assets["frameName.png"]`
this[frame] = file.frames[frame];
//Get a reference to the source so that it will be easy for
//us to access it later
this[frame].source = image;
});
//Alert the load handler that the file has loaded
loadHandler();
};
//Load the tileset image
let image = new Image();
image.addEventListener("load", imageLoadHandler, false);
image.src = imageSource;
},
loadSound(source, loadHandler) {
console.log("loadSound called – see Chapter 10 for details");
}
};
assets.load([
"4.jpg",
"France.ttf",
"json.json"
]).then(() => setup());
function setup() {
//Initialize the game
console.log('done')
}
将包含：
蔬菜，牛肉，鸡肉，饮料
答案 0 :(得分：1)
您可以使用List.addAll()，但 还必须在插入后删除Foods条目。
goods.remove("Foods"); // remove by object (String name)
goods.addAll(1, foods);
来自List.addAll(int index, Collection c)的{{3}}：
从指定位置开始，将指定集合中的所有元素插入此列表。将当前位置的元素（如果有）和任何后续元素向右移动（增加其索引）。
答案 1 :(得分：0)
goods.addAll(1, foods);
goods.remove("Foods");会奏效。