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The Checker Framework enhances Java's type system to make it more powerful and useful. This lets software developers detect and prevent errors in their Java programs. The Checker Framework includes compiler plug-ins ("checkers") that find bugs or verify their absence. It also permits you to write your own compiler plug-ins.

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package org.checkerframework.dataflow.expression;

import java.util.List;
import org.checkerframework.checker.nullness.qual.Nullable;
import org.checkerframework.checker.nullness.qual.PolyNull;
import org.plumelib.util.CollectionsPlume;

/**
 * This class calls {@link #convert(JavaExpression)} on each subexpression of the {@link
 * JavaExpression} and returns a new {@code JavaExpression} built from the result of calling {@code
 * convert} on each subexpression. (If an expression has no subexpression, then the expression
 * itself is returned.)
 *
 * This class makes it easy to implement a subclass that converts subexpressions of a {@link
 * JavaExpression} based on which kind of {@code JavaExpression} the subexpression is. Subclasses
 * should override the visit method of kinds of JavaExpressions to convert.
 */
public abstract class JavaExpressionConverter extends JavaExpressionVisitor {

  /**
   * Converts {@code javaExpr} and returns the resulting {@code JavaExpression}.
   *
   * @param javaExpr the expression to convert
   * @return the converted expression
   */
  public JavaExpression convert(JavaExpression javaExpr) {
    return super.visit(javaExpr, null);
  }

  /**
   * Converts all the expressions in {@code list} and returns the resulting list.
   *
   * @param list the list of expressions to convert
   * @return the list of converted expressions
   */
  public List<@PolyNull JavaExpression> convert(List<@PolyNull JavaExpression> list) {
    return CollectionsPlume.mapList(
        (@PolyNull JavaExpression expression) -> {
          // Can't use a ternary operator because of:
          // https://github.com/typetools/checker-framework/issues/1170
          if (expression == null) {
            return null;
          }
          return convert(expression);
        },
        list);
  }

  @Override
  protected JavaExpression visitArrayAccess(ArrayAccess arrayAccessExpr, Void unused) {
    JavaExpression array = convert(arrayAccessExpr.getArray());
    JavaExpression index = convert(arrayAccessExpr.getIndex());
    return new ArrayAccess(arrayAccessExpr.type, array, index);
  }

  @Override
  protected JavaExpression visitArrayCreation(ArrayCreation arrayCreationExpr, Void unused) {
    List<@Nullable JavaExpression> dims = convert(arrayCreationExpr.getDimensions());
    List inits = convert(arrayCreationExpr.getInitializers());
    return new ArrayCreation(arrayCreationExpr.getType(), dims, inits);
  }

  @Override
  protected JavaExpression visitBinaryOperation(BinaryOperation binaryOpExpr, Void unused) {
    JavaExpression left = convert(binaryOpExpr.getLeft());
    JavaExpression right = convert(binaryOpExpr.getRight());
    return new BinaryOperation(
        binaryOpExpr.getType(), binaryOpExpr.getOperationKind(), left, right);
  }

  @Override
  protected JavaExpression visitClassName(ClassName classNameExpr, Void unused) {
    return classNameExpr;
  }

  @Override
  protected JavaExpression visitFieldAccess(FieldAccess fieldAccessExpr, Void unused) {
    JavaExpression receiver = convert(fieldAccessExpr.getReceiver());
    return new FieldAccess(receiver, fieldAccessExpr.getType(), fieldAccessExpr.getField());
  }

  @Override
  protected JavaExpression visitFormalParameter(FormalParameter parameterExpr, Void unused) {
    return parameterExpr;
  }

  @Override
  protected JavaExpression visitLocalVariable(LocalVariable localVarExpr, Void unused) {
    return localVarExpr;
  }

  @Override
  protected JavaExpression visitMethodCall(MethodCall methodCallExpr, Void unused) {
    JavaExpression receiver = convert(methodCallExpr.getReceiver());
    List args = convert(methodCallExpr.getArguments());
    return new MethodCall(methodCallExpr.getType(), methodCallExpr.getElement(), receiver, args);
  }

  @Override
  protected JavaExpression visitThisReference(ThisReference thisExpr, Void unused) {
    return thisExpr;
  }

  @Override
  protected JavaExpression visitUnaryOperation(UnaryOperation unaryOpExpr, Void unused) {
    JavaExpression operand = convert(unaryOpExpr.getOperand());
    return new UnaryOperation(unaryOpExpr.getType(), unaryOpExpr.getOperationKind(), operand);
  }

  @Override
  protected JavaExpression visitUnknown(Unknown unknownExpr, Void unused) {
    return unknownExpr;
  }

  @Override
  protected JavaExpression visitValueLiteral(ValueLiteral literalExpr, Void unused) {
    return literalExpr;
  }
}