ProhibitUnusedPrivateConstructorCheck.java
/*
* Copyright (c) 2011-2025 Yegor Bugayenko
*
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package com.qulice.checkstyle;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
import java.util.LinkedList;
import java.util.List;
/**
* Checks that constructor, declared as private class is used more than once.
*
* @since 0.3
*/
public final class ProhibitUnusedPrivateConstructorCheck extends AbstractCheck {
@Override
public int[] getDefaultTokens() {
return new int[] {TokenTypes.CLASS_DEF};
}
@Override
public int[] getAcceptableTokens() {
return this.getDefaultTokens();
}
@Override
public int[] getRequiredTokens() {
return this.getDefaultTokens();
}
@Override
public void visitToken(final DetailAST ast) {
final DetailAST objblock = ast.findFirstToken(TokenTypes.OBJBLOCK);
if (objblock != null) {
this.checkConstructors(objblock);
}
}
/**
* Collects all private constructors in a given object block.
*
* @param objblock Node which contains constructors
* @return List of DetailAST nodes representing the private constructors
*/
private static List<DetailAST> collectPrivateConstructors(final DetailAST objblock) {
final List<DetailAST> prvctors = new LinkedList<>();
final DetailAST firstchld = objblock.getFirstChild();
for (DetailAST child = firstchld; child != null; child = child.getNextSibling()) {
if (child.getType() == TokenTypes.CTOR_DEF && isPrivate(child)) {
prvctors.add(child);
}
}
return prvctors;
}
/**
* Checks if a private constructor is used in the object block.
*
* @param privatector Node representing the private constructor
* @param objblock Node which contains constructors
* @return True if the private constructor is used, False otherwise
*/
private static boolean isPrivateConstructorUsed(
final DetailAST privatector, final DetailAST objblock) {
return
isPrivateCtorUsedInOtherCtors(privatector, objblock)
||
isPrivateCtorUsedInMethods(privatector, objblock);
}
/**
* Checks if a private constructor is used in other constructors.
*
* @param privatector Node representing the private constructor
* @param objblock Node containing constructors
* @return True if the private constructor is used, False otherwise
*/
private static boolean isPrivateCtorUsedInOtherCtors(
final DetailAST privatector, final DetailAST objblock) {
final List<DetailAST> allctors = collectAllConstructors(objblock);
return allctors.stream()
.anyMatch(
otherCtor -> otherCtor != privatector
&&
isCallingConstructor(otherCtor, privatector));
}
/**
* Checks if a private constructor is used in methods of the object block.
*
* @param privatector Node representing the private constructor
* @param objblock Node containing methods
* @return True if the private constructor is used, False otherwise
*/
private static boolean isPrivateCtorUsedInMethods(
final DetailAST privatector, final DetailAST objblock) {
boolean result = false;
final DetailAST firstchld = objblock.getFirstChild();
for (DetailAST child = firstchld; child != null; child = child.getNextSibling()) {
if (child.getType() == TokenTypes.METHOD_DEF
&&
isCallingConstructor(child, privatector)) {
result = true;
break;
}
}
return result;
}
/**
* Collects all constructors in a given object block.
*
* @param objblock Node which contains constructors
* @return List of DetailAST nodes representing all the constructors
*/
private static List<DetailAST> collectAllConstructors(final DetailAST objblock) {
final List<DetailAST> allctors = new LinkedList<>();
final DetailAST firstchld = objblock.getFirstChild();
for (DetailAST child = firstchld; child != null; child = child.getNextSibling()) {
if (child.getType() == TokenTypes.CTOR_DEF) {
allctors.add(child);
}
}
return allctors;
}
/**
* Returns true if specified node has modifiers of type
* <code>PRIVATE</code>.
*
* @param node Node to check.
* @return True if specified node contains modifiers of type
* <code>PRIVATE</code>, else returns <code>false</code>.
*/
private static boolean isPrivate(final DetailAST node) {
final DetailAST modifiers = node.findFirstToken(TokenTypes.MODIFIERS);
return modifiers.getChildCount(TokenTypes.LITERAL_PRIVATE) > 0;
}
private static boolean isCallingConstructor(
final DetailAST methodorctor, final DetailAST targetctor) {
boolean result = false;
final DetailAST body = methodorctor.findFirstToken(TokenTypes.SLIST);
if (body != null) {
DetailAST stmt = body.getFirstChild();
while (stmt != null && !result) {
result = isMatchingConstructorCall(stmt, targetctor);
stmt = stmt.getNextSibling();
}
}
return result;
}
private static boolean isMatchingConstructorCall(
final DetailAST stmt, final DetailAST targetctor) {
return
stmt.getType() == TokenTypes.CTOR_CALL
&&
matchesConstructorSignature(stmt, targetctor);
}
private static boolean matchesConstructorSignature(
final DetailAST callexpr, final DetailAST ctor) {
final DetailAST callparams = callexpr.findFirstToken(TokenTypes.ELIST);
final DetailAST ctorparams = ctor.findFirstToken(TokenTypes.PARAMETERS);
return parametersCountMatch(callparams, ctorparams);
}
private static boolean parametersCountMatch(
final DetailAST callparams, final DetailAST ctorparams) {
final int ncallparams = callparams.getChildCount(TokenTypes.EXPR);
final int nctorparams = ctorparams.getChildCount(TokenTypes.PARAMETER_DEF);
return ncallparams == nctorparams;
}
/**
* Checks if private constructors are used.
* Logs a message if a private constructor is not used.
*
* @param objblock Node which contains constructors
*/
private void checkConstructors(final DetailAST objblock) {
final List<DetailAST> prvctors = collectPrivateConstructors(objblock);
for (final DetailAST ctor : prvctors) {
if (!isPrivateConstructorUsed(ctor, objblock)) {
this.log(ctor.getLineNo(), "Unused private constructor.");
}
}
}
}