Lambda表達(dá)式在Java 8中引入，用於簡化函數(shù)式接口的實例編寫。 1. 其基本語法為(parameters) -> { body }，可根據(jù)情況省略參數(shù)類型或括號，如無參數(shù)用() -> System.out.println("Hello")，一個參數(shù)用x -> System.out.println(x)，多個參數(shù)用(x, y) -> xy；2. 可將lambda賦值給函數(shù)式接口如Runnable、Consumer或Function，替代匿名類寫法，提升可讀性；3. 常與集合和Stream API結(jié)合使用，如forEach、filter、map等操作，使代碼更簡潔清晰；4. 結(jié)合類型推斷可省略參數(shù)類型，提升代碼簡潔性；5. 使用方法引用（如System.out::println）代替僅調(diào)用單個方法的lambda，進(jìn)一步減少冗餘代碼。合理使用lambda可提升Java開發(fā)效率與代碼質(zhì)量。

Lambda expressions were introduced in Java 8, and they brought a more concise way to write instances of functional interfaces —interfaces with only one abstract method. If you're looking to simplify your code or work with streams and modern Java features, lambdas are essential.

Here's how to use them effectively.

Understanding the Basic Syntax

The basic structure of a lambda expression is:

 (parameters) -> { body }

Depending on the situation, parts of this can be omitted for brevity.

• No parameters : () -> System.out.println("Hello")
• One parameter : x -> System.out.println(x)
• Multiple parameters : (x, y) -> xy

You can assign these directly to functional interfaces like Runnable , Consumer , or Function .

For example:

 Runnable r = () -> System.out.println("Running...");

This replaces the older anonymous class style:

 Runnable r = new Runnable() {
    public void run() {
        System.out.println("Running...");
    }
};

It's cleaner and easier to read, especially when passing behavior as arguments.

Using Lambdas with Collections and Streams

One of the most common uses of lambda expressions is with Java Streams , which were also introduced in Java 8.

If you have a list and want to process each element, instead of writing a loop, you can do something like:

 List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
names.forEach(name -> System.out.println(name));

Or filter elements:

 names.stream()
     .filter(name -> name.startsWith("A"))
     .forEach(System.out::println);

This makes it easy to chain operations and keep your logic clear.

Some key interfaces to know when working with lambdas and streams:

• Predicate<T> – used for filtering ( test method)
• Function<T, R> – used for mapping ( apply )
• Consumer<T> – for side effects ( accept )
• Supplier<T> – for lazy evaluation ( get )

Each of these can be implemented using a lambda, without needing custom classes.

Leveraging Type Inference and Method References

Java can often infer types from context, so you don't always need to specify them explicitly.

Instead of:

 List<String> filtered = names.stream()
    .filter((String name) -> name.length() > 3)
    .toList();

You can just write:

 List<String> filtered = names.stream()
    .filter(name -> name.length() > 3)
    .toList();

Also, if your lambda just calls an existing method, you can replace it with a method reference :

 names.forEach(System.out::println);

Which is shorter than:

 names.forEach(x -> System.out.println(x));

Method references come in a few forms:

• ClassName::staticMethod
• object::instanceMethod
• ClassName::instanceMethod (used when the first argument is the instance)

They help reduce visual noise and improve readability.

Using lambda expressions doesn't have to feel complex. Start with simple cases like replacing anonymous classes or iterating over collections, and gradually move into more advanced stream operations. Just remember to keep your lambdas short and focused — ideally doing only one thing.

Once you get used to them, they become a natural part of your Java toolkit.

基本上就這些。

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