# Replace Stream Collect By ToList
# Description
Java 16 introduced Stream.toList()
(opens new window) as a shorthand method for converting a Stream into an unmodifiable List.
This rule replaces invocations of collect(Collectors.toUnmodifiableList())
on streams by invocations of the new method stream.toList()
.
In case Collectors.toList()
is used as a collector, the rule makes additional verifications whether the generated list is modified by the context or not.
In the latter case, invocations of collect(Collectors.toList())
on streams are also replaced by invocations of toList()
.
Thus the code is simplified and readability is improved.
Requirements
- Java 16
# Benefits
Removes code clutter. Improves readability.
# Tags
# Code Changes
# Using Collectors.toUnmodifiableList()
Pre
List<String> List = collection
.stream()
.map(function)
.filter(predicate)
.collect(Collectors.toUnmodifiableList());
Post
List<String> List = collection
.stream()
.map(function)
.filter(predicate)
.toList();
# Argument of Collections.unmodifiableList(...)
Pre
return Collections.unmodifiableList(collection
.stream()
.map(function)
.filter(predicate)
.collect(Collectors.toList()));
Post
return Collections.unmodifiableList(collection
.stream()
.map(function)
.filter(predicate)
.toList());
# Using Collectors.toList()
Pre
void sendMails(List<User>users) {
List<String> emails = users.stream()
.map(User::getMail)
.collect(Collectors.toList());
for (String email : emails) {
validate(email);
send(email);
}
}
Post
void sendMails(List<User>users) {
List<String> emails = users.stream()
.map(User::getMail)
.toList();
for (String email : emails) {
validate(email);
send(email);
}
}
# Argument of Collections.min(...)
Pre
int min = Collections.min(collection
.stream()
.map(function)
.filter(predicate)
.collect(Collectors.toList()));
Post
int min = Collections.min(collection
.stream()
.map(function)
.filter(predicate)
.toList());
# Argument of List.copyOf(...)
Pre
return List.copyOf(collection
.stream()
.map(function)
.filter(predicate)
.collect(Collectors.toList()));
Post
return List.copyOf(collection
.stream()
.map(function)
.filter(predicate)
.toList());
# Argument of list.addAll(...)
Pre
list.addAll(collection
.stream()
.map(function)
.filter(predicate)
.collect(Collectors.toList()));
Post
list.addAll(collection
.stream()
.map(function)
.filter(predicate)
.toList());
# Enhanced For Loop with Stream.collect(...)
Pre
for (String s : collection
.stream()
.map(function)
.filter(predicate)
.collect(Collectors.toList())) {
//...
}
Post
for (String s : collection
.stream()
.map(function)
.filter(predicate)
.toList()) {
//...
}
Use a Java Refactoring Tool
No license required
You can review this refactoring on your code without a license by installing jSparrow to your Eclipse IDE. Install the plug-in from Eclipse IDE: Eclipse Marketplace.
System-wide Refactoring
Do you want to automate this refactoring (and many more) to your system-wide code? The automatic application of this system-wide refactoring can be unlocked by acquiring your jSparrow license.
# Properties
Property | Value |
---|---|
Rule ID | ReplaceStreamCollectByToList |
First seen in jSparrow version | 4.4.0 |
Minimum Java version | 16 |
Remediation cost | 2 min |