Lernen Method References | Advanced Lambda Usage

Method references provide a concise way to refer to existing methods or constructors as alternatives to writing full lambda expressions. They use a double colon (::) syntax to point directly to a method or constructor, making your code more readable and often less verbose. There are three main kinds of method references in Java:

Static method references: refer to static methods of a class using the syntax ClassName::staticMethodName;
Instance method references: refer to instance methods of a particular object or of an arbitrary object of a particular type using the syntax instance::instanceMethodName or ClassName::instanceMethodName;
Constructor references: refer to a class constructor using the syntax ClassName::new.

Using method references can make your code easier to read and maintain, especially when the lambda expression simply calls an existing method.

Main.java


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// File: Main.java
package com.example;

import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import java.util.function.Supplier;

public class Main {
    public static void main(String[] args) {
        // Static method reference
        Function<String, Integer> parseInt = Integer::parseInt;
        System.out.println(parseInt.apply("123")); // prints 123

        // Instance method reference of a particular object
        String myString = "hello";
        Supplier<String> toUpper = myString::toUpperCase;
        System.out.println(toUpper.get()); // prints HELLO

        // Instance method reference of an arbitrary object of a particular type
        List<String> words = Arrays.asList("apple", "banana", "cherry");
        words.forEach(System.out::println);

        // Constructor reference
        Supplier<StringBuilder> stringBuilderSupplier = StringBuilder::new;
        StringBuilder sb = stringBuilderSupplier.get();
        sb.append("Lambda");
        System.out.println(sb.toString()); // prints Lambda
    }
}

Method references are often used as a shorthand for lambda expressions that just call a single method. For example, list.forEach(s -> System.out.println(s)); can be replaced with list.forEach(System.out::println);. Method references can only be used when the parameter types of the functional interface match the method signature being referenced. In general, you should use a method reference when it improves clarity and conciseness, but stick with a lambda when you need to add logic or pass parameters in a way that does not directly match a method signature.

Main.java


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package com.example;

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> fruits = Arrays.asList("apple", "banana", "kiwi", "cherry");
        // Using a method reference to sort by string length
        fruits.sort(Comparator.comparingInt(String::length));
        System.out.println(fruits); // prints [kiwi, apple, banana, cherry]
    }
}

1. Which symbol is used to write a method reference in Java?

2. What is the main difference between a static method reference and an instance method reference?

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Abschnitt 2. Kapitel 1

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Static method references: refer to static methods of a class using the syntax ClassName::staticMethodName;
Instance method references: refer to instance methods of a particular object or of an arbitrary object of a particular type using the syntax instance::instanceMethodName or ClassName::instanceMethodName;
Constructor references: refer to a class constructor using the syntax ClassName::new.

Using method references can make your code easier to read and maintain, especially when the lambda expression simply calls an existing method.

Main.java


              12345678910111213141516171819202122232425262728293031
            
// File: Main.java
package com.example;

import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import java.util.function.Supplier;

public class Main {
    public static void main(String[] args) {
        // Static method reference
        Function<String, Integer> parseInt = Integer::parseInt;
        System.out.println(parseInt.apply("123")); // prints 123

        // Instance method reference of a particular object
        String myString = "hello";
        Supplier<String> toUpper = myString::toUpperCase;
        System.out.println(toUpper.get()); // prints HELLO

        // Instance method reference of an arbitrary object of a particular type
        List<String> words = Arrays.asList("apple", "banana", "cherry");
        words.forEach(System.out::println);

        // Constructor reference
        Supplier<StringBuilder> stringBuilderSupplier = StringBuilder::new;
        StringBuilder sb = stringBuilderSupplier.get();
        sb.append("Lambda");
        System.out.println(sb.toString()); // prints Lambda
    }
}

Main.java


              123456789101112131415
            
package com.example;

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> fruits = Arrays.asList("apple", "banana", "kiwi", "cherry");
        // Using a method reference to sort by string length
        fruits.sort(Comparator.comparingInt(String::length));
        System.out.println(fruits); // prints [kiwi, apple, banana, cherry]
    }
}

1. Which symbol is used to write a method reference in Java?

2. What is the main difference between a static method reference and an instance method reference?

War alles klar?

Danke für Ihr Feedback!

Abschnitt 2. Kapitel 1