Use Pattern Matching for Instanceof

Description

This rule replaces instanceof expressions by Pattern Matching for instanceof (opens new window) introduced in Java 16.

It is very common for Java programs to contain logic that combines type checking using instanceof with explicit type casting. Naturally, an instanceof expression is followed by a local variable declaration initialized with a casting expression. Pattern Matching for instanceof combines these three steps (i.e., type checking, variable declaration, and type casting) into a single step, thus reducing boilerplate code and eliminating sources of errors.

Requirements

• Java 16

Benefits

Removes code clutter. Improves readability.

Tags

Tags

Java 16, Old Language Constructs, Readability

Code Changes

Pattern Matching in If Statement

Pre

if(o instanceof String) {
    String value = (String)o;		
    showValue(value);
}

Post

if(o instanceof String value) {
    showValue(value);
}

Pattern Matching in If-Then-Else Statement

Pre

if (!(o instanceof String)) {
    dontShowValue();
} else {
    String value = (String) o;
    showValue(value);
}

Post

if (!(o instanceof String value)) {
    dontShowValue();
} else {
    showValue(value);
}

Pattern Matching with Return Statement

Pre

if (!(o instanceof String)) {
    dontShowValue();
    return false;
}
String value = (String)o;
showValue(value);
return "Olympics 2020".equals(value);

Post

if (!(o instanceof String value)) {
    dontShowValue();
    return false;
}
showValue(value);
return "Olympics 2020".equals(value);

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Properties

Property	Value
Rule ID	UsePatternMatchingForInstanceof
First seen in jSparrow version	4.2.0
Minimum Java version	16
Remediation cost	5 min