Method References (Class::method, instance::method, Class::new)0%

Stream Pipeline Lifecycle: Source -> Intermediate Operations -> Terminal Operation

Method References (Class::method, instance::method, Class::new)

Advanced14 min read•Updated: 2025-01-15

🎯 Method References (Class::method, instance::method, Class::new)

Introduction

When a lambda expression simply calls an existing method without adding extra logic, Java provides a cleaner, more readable shorthand: the Method Reference using the double-colon (::) operator.

🏷️ The 4 Types of Method References

1┌──────────────────────────────┬──────────────────────────┬────────────────────────┐
2│ Type                         │ Syntax                   │ Equivalent Lambda      │
3├──────────────────────────────┼──────────────────────────┼────────────────────────┤
4│ 1. Static Method             │ ContainingClass::staticM │ (args) -> Class.m(args)│
5│ 2. Instance of Arbitrary Obj │ ContainingType::method   │ (obj, args) -> obj.m() │
6│ 3. Instance of Specific Obj  │ instanceRef::method      │ (args) -> instance.m() │
7│ 4. Constructor               │ ClassName::new           │ (args) -> new Class()  │
8└──────────────────────────────┴──────────────────────────┴────────────────────────┘

💻 1. Static Method References (`Class::staticMethod`)

1// Lambda:
2Function<String, Integer> parser1 = s -> Integer.parseInt(s);
3 
4// Method Reference:
5Function<String, Integer> parser2 = Integer::parseInt;

💻 2. Instance Method of an Arbitrary Object (`Class::instanceMethod`)

Here the first parameter of the functional interface becomes the target object on which the method is called:

1List<String> names = List.of("aarav", "priya", "rohit");
2 
3// Lambda:
4names.stream().map(s -> s.toUpperCase()).forEach(System.out::println);
5 
6// Method Reference:
7names.stream().map(String::toUpperCase).forEach(System.out::println);

💻 3. Instance Method of a Specific Existing Object (`instance::method`)

1PrintStream out = System.out;
2 
3// Lambda:
4Consumer<String> logger1 = s -> out.println(s);
5 
6// Method Reference:
7Consumer<String> logger2 = out::println;

💻 4. Constructor References (`Class::new`)

1// Lambda:
2Supplier<List<String>> listSupplier1 = () -> new ArrayList<>();
3 
4// Constructor Reference:
5Supplier<List<String>> listSupplier2 = ArrayList::new;
6 
7// With arguments:
8Function<String, Student> studentFactory = Student::new;
9Student s = studentFactory.apply("Vikram Rathore");

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🏷️ The 4 Types of Method References

1┌──────────────────────────────┬──────────────────────────┬────────────────────────┐
2│ Type                         │ Syntax                   │ Equivalent Lambda      │
3├──────────────────────────────┼──────────────────────────┼────────────────────────┤
4│ 1. Static Method             │ ContainingClass::staticM │ (args) -> Class.m(args)│
5│ 2. Instance of Arbitrary Obj │ ContainingType::method   │ (obj, args) -> obj.m() │
6│ 3. Instance of Specific Obj  │ instanceRef::method      │ (args) -> instance.m() │
7│ 4. Constructor               │ ClassName::new           │ (args) -> new Class()  │
8└──────────────────────────────┴──────────────────────────┴────────────────────────┘

💻 2. Instance Method of an Arbitrary Object (Class::instanceMethod)

Here the first parameter of the functional interface becomes the target object on which the method is called:

1List<String> names = List.of("aarav", "priya", "rohit");
2 
3// Lambda:
4names.stream().map(s -> s.toUpperCase()).forEach(System.out::println);
5 
6// Method Reference:
7names.stream().map(String::toUpperCase).forEach(System.out::println);

Previous Lesson

Next Lesson

Lambda Expression Syntax, Scope, and Variable Capture

Stream Pipeline Lifecycle: Source -> Intermediate Operations -> Terminal Operation

🎯 Method References (Class::method, instance::method, Class::new)

Introduction

🏷️ The 4 Types of Method References

💻 1. Static Method References (Class::staticMethod)

💻 2. Instance Method of an Arbitrary Object (Class::instanceMethod)

💻 3. Instance Method of a Specific Existing Object (instance::method)

💻 4. Constructor References (Class::new)

Stream Pipeline Lifecycle: Source -> Intermediate Operations -> Terminal Operation

Related Lessons

Practice Quiz

Loading Page Content...

🎯 Method References (Class::method, instance::method, Class::new)

Introduction

🏷️ The 4 Types of Method References

💻 1. Static Method References (Class::staticMethod)

💻 2. Instance Method of an Arbitrary Object (Class::instanceMethod)

💻 3. Instance Method of a Specific Existing Object (instance::method)

💻 4. Constructor References (Class::new)

Stream Pipeline Lifecycle: Source -> Intermediate Operations -> Terminal Operation

Related Lessons

Practice Quiz

💻 1. Static Method References (`Class::staticMethod`)

💻 2. Instance Method of an Arbitrary Object (`Class::instanceMethod`)

💻 3. Instance Method of a Specific Existing Object (`instance::method`)

💻 4. Constructor References (`Class::new`)

💻 1. Static Method References (`Class::staticMethod`)

💻 2. Instance Method of an Arbitrary Object (`Class::instanceMethod`)

💻 3. Instance Method of a Specific Existing Object (`instance::method`)

💻 4. Constructor References (`Class::new`)