java append 方法

Java StringBuilder

Java StringBuilder is a class in the Java API that allows you to manipulate strings in an efficient and flexible way. One important method in the StringBuilder class is the append() method, which is used to concatenate strings.

The append() method accepts different types of parameters such as integers, floats, doubles, characters, strings, and even other StringBuilder objects. When you call the append() method with a parameter, it returns the same StringBuilder object, which means it can be chained with subsequent append() method calls.

For example, the following code snippet demonstrates how to concatenate strings using the append() method:

```

StringBuilder sb = new StringBuilder();

sb.append("Hello").append(" ").append("World");

The StringBuilder object sb now contains the concatenated string "Hello World".

Java StringBuffer

Java StringBuffer is another class in the Java API that is similar to StringBuilder. The main difference between StringBuffer and StringBuilder is that StringBuffer is thread-safe, meaning it can be accessed by multiple threads simultaneously without producing any incorrect results.

The append() method in StringBuffer works similarly to the append() method in StringBuilder. However, since StringBuffer is thread-safe, it has some overhead that makes it slower than StringBuilder. In general, if you don't need thread-safety, it's better to use StringBuilder instead of StringBuffer.

Java String Concatenation

Before the introduction of StringBuilder and StringBuffer, string concatenation in Java was done using the "+" operator. While this method works fine for small strings, it performs poorly for large strings because each concatenation creates a new string object in memory.

For example, consider the following code:

String str = "a";

for (int i = 0; i < 10000; i++) {

str += "a";

}

In this code, the "+" operator creates 10,000 new string objects, which can cause performance issues. To avoid this problem, you can use the StringBuilder or StringBuffer class instead.

In conclusion, the append() method in Java is a powerful tool for concatenating strings efficiently and flexibly. You can use either StringBuilder or StringBuffer depending on your needs, and avoid the performance problems associated with string concatenation using the "+" operator.