何时适合使用'new'关键字？ [英] When is the appropriate time to use the 'new' keyword?

问题描述

何时需要在Java中使用 new 关键字。我知道你应该在创建像这样的对象的实例时使用它：

When is it necessary to use the new keyword in Java. I know you are supposed to use it when you create an instance of an object like this:

TextView textView = new TextView(this);

有时在代码中我注意到 new isn使用了，我感到困惑..
在这行代码中：

Sometimes in code I notice that new isn't used and I get confused.. In this line of code:

    AssetManager assetManager = getAssets();

为什么不像这样创建AssetManager的实例：

Why isn't an instance of the AssetManager created like this:

AssetManager assetManager = new AssetManager();

然后设置为等于getAssests（）？

then it is set equal to getAssests()?

何时应该使用 new ？

谢谢！

推荐答案

在第一次显式创建对象时使用new关键字。然后不需要使用getter方法new获取对象，因为该对象已经存在于内存中，因此不需要重新创建。

You use the new keyword when an object is being explicitly created for the first time. Then fetching an object using a getter method new is not required because the object already exists in memory, thus does not need to be recreated.

如果你想要更详细的描述新访问 oracle docs

if you want a more detailed description of new visit the oracle docs

一个对象需要'new'关键字，如果它是null（这对于未初始化很有意义）。

An object will need the 'new' keyword if it is null (which is fancy for not initialized).

编辑：

在当前情况下，这将始终打印需要新的。

This will always print "needs new" under the current circumstances.

Object mObj = null;
if (mObj == null)
    System.out.println("needs new");
else
    System.out.println("does NOT need new");

OUTPUTS: needs new

所以要修复它，你会做点什么喜欢：

So to fix it, you would do something like:

Object mObj = new Object();
if (mObj == null)
    System.out.println("needs new");
else
    System.out.println("does NOT need new");
OUTPUTS: does NOT need new

在这种情况下，我们总是会看到不是需要新的

And under those circumstances we will always see "does NOT need neW"

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