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Java Refactoring

Table of Content

Introduction

The goal of the Java program refactoring is to make system-wide code changes without affecting the behavior of the program. The Java Language Support for VSCODE_ENV_APPNAME_PLACEHOLDER provides assistance in easily refactoring code.

Invoke refactoring

Refactoring commands are available from the context menu of the editor. Select the element you want to refactor, right-click to open the context menu and choose Refactor...:

menu

Then you will see all the available refactoring options.

Assign to variable

Assigns an expression to a local variable or a field.

Example

Before

Arrays.asList("apple", "lemon", "banana");

After

List<String> fruits = Arrays.asList("apple", "lemon", "banana");

Change modifiers to final

Adds final modifier to all the variables and parameters in the current source file.

Example

Before

public class Clazz {
  public void method(int value) {
    boolean notValid = value > 5;
    if (notValid) {
      // do something
    }
  }
}

After

public class Clazz {
  public void method(final int value) {
    final boolean notValid = value > 5;
    if (notValid) {
      // do something
    }
  }
}

Convert anonymous to nested class

Converts an anonymous inner class to a member class.

Example

Let's convert the anonymous class Interface(){...} to a member of the class Clazz.

Before

public class Clazz {
  public Interface method() {
    final boolean isValid = true;
    return new Interface() {
      public boolean isValid() {
        return isValid;
      }
    };
  }
}

After

public class Clazz {
  private final class MyInterface extends Interface {
    private final boolean isValid;

    private MyInterface(boolean isValid) {
      this.isValid = isValid;
    }

    public boolean isValid() {
      return isValid;
    }
  }

  public Interface method() {
    final boolean isValid = true;
    return new MyInterface(isValid);
  }
}

Convert to anonymous class creation

Converts lambda expression to anonymous class creation.

Example

The variable runnable is assigned with a lambda expression. Let's convert it to an anonymous class creation.

Before

public void method() {
  Runnable runnable = () -> {
    // do something
  };
}

After

public void method() {
  Runnable runnable = new Runnable() {
    @Override
    public void run() {
      // do something
    }
  };
}

Also see: Convert to lambda expression

Convert to enhanced for loop

Converts the simple for loop to for-each style.

Example

Before

public void order(String[] books) {
  for (int i = 0; i < books.length; i++) {
    // do something
  }
}

After

public void order(String[] books) {
  for (String book : books) {
    // do something
  }
}

Convert to lambda expression

Converts an anonymous class creation to the lambda expression.

Example

Let's convert the anonymous class Runnable(){...} to a lamda expression.

Before

public void method() {
  Runnable runnable = new Runnable(){
    @Override
    public void run() {
      // do something
    }
  };
}

After

public void method() {
    Runnable runnable = () -> {
      // do something
    };
  }

Also see: Convert to anonymous class creation

Convert to static import

Converts the field or method to static import.

Example

Let's transform the Assert.assertEquals() invocation to a static import.

Before

import org.junit.Assert;
...
public void test() {
  Assert.assertEquals(expected, actual);
}

After

import static org.junit.Assert.assertEquals;
...
public void test() {
  assertEquals(expected, actual);
}

Extract to constant

Creates a static final field from the selected expression and substitutes a field reference, then rewrites other places where the same expression occurs.

Examples

Let's extract the value of π: 3.14 to a constant.

Before

public double getArea(double r) {
  return 3.14 * r * r;
}

After

private static final double PI = 3.14;

public double getArea(double r) {
  return PI * r * r;
}

Also see: Inline constant

Extract to field

Declares a new field and initializes it with the selected expression. The original expression is replaced with the usage of the field.

Examples

Let's extract the variable area to a field of the class Square.

Before

class Square {
  public void calculateArea() {
    int height = 1;
    int width = 2;
    int area = height * width;
  }
}

After

class Square {
  private int area;

  public void calculateArea() {
    int height = 1;
    int width = 2;
    area = height * width;
  }
}

Extract to method

Creates a new method containing the statements or expressions currently selected and replaces the selection with a reference to the new method. This feature is useful for cleaning up lengthy, cluttered, or overly-complicated methods.

Examples

Let's extract the expression height * width to a new method.

Before

public void method() {
  int height = 1;
  int width = 2;
  int area = height * width;
}

After

public void method() {
  int height = 1;
  int width = 2;
  int area = getArea(height, width);
}

private int getArea(int height, int width) {
  return height * width;
}

Also see: Inline method

Extract to local variable

Creates a new variable assigned to the expression currently selected and replaces the selection with a reference to the new variable.

Examples

Let's extract the expression platform.equalsIgnoreCase("MAC") to a new variable.

Before

public void method() {
  if (platform.equalsIgnoreCase("MAC")) {
    // do something
  }
}

After

public void method() {
  boolean isMac = platform.equalsIgnoreCase("MAC");
  if (isMac) {
    // do something
  }
}

Also see: Inline local variable

Inline constant

Replaces a constant reference with its defined value.

Examples

Let's replace the constant PI to its defined value: 3.14.

Before

private static final double PI = 3.14;

public double getArea(double r) {
  return PI * r * r;
}

After

private static final double PI = 3.14;

public double getArea(double r) {
  return 3.14 * r * r;
}

Also see: Extract to constant

Inline local variable

Replaces redundant variable usage with its initializer.

Examples

Let's replace the variable isMac directly to the boolean expression.

Before

public void method() {
  boolean isMac = platform.equalsIgnoreCase("MAC");
  if (isMac) {
    // do something
  }
}

After

public void method() {
  if (platform.equalsIgnoreCase("MAC")) {
    // do something
  }
}

Also see: Extract to local variable

Inline method

Replaces calls to the method with the method’s body.

Example

Let's replace the method getArea(int height, int width) directly to the expression height * width.

Before

public void method() {
  int height = 1;
  int width = 2;
  int area = getArea(height, width);
}

private int getArea(int height, int width) {
  return height * width;
}

After

public void method() {
  int height = 1;
  int width = 2;
  int area = height * width;
}

Also see: Extract to method

Introduce Parameter

Replaces an expression with a reference to a new method parameter, and updates all callers of the method to pass the expression as the value of that parameter.

Example

Let's introduce a new parameter for the method public void addUser().

Before

public void buildRegistry() {
  addUser();
}

public void addUser() {
  fUsers.add("Administrator");
}

After

public void buildRegistry() {
  addUser("Administrator");
}

public void addUser(String name) {
  fUsers.add(name);
}

Invert conditions

Inverts the boolean expression in the conditions.

Example

Let's invert the boolean expression in the if statement.

Before

public void method(int value) {
  if (value > 5 && value < 15) {
    // do something
  }
}

After

public void method(int value) {
  if (value <= 5 || value >= 15) {
    // do something
  }
}

Invert local variable

Inverts the local boolean variable.

Example

Let's invert the variable valid.

Before

public void method(int value) {
  boolean valid = value > 5 && value < 15;
}

After

public void method(int value) {
  boolean notValid = value <= 5 || value >= 15;
}

Move

Moves the selected elements and corrects all references to the elements (also in other files). Available actions are:

  • Move class to another package
  • Move static or instance method to another class
  • Move inner class to a new file

Examples

Let's move the static method print() from class Office to class Printer.

Before

public class Office {
  public static void main(String[] args) {
    print();
  }

  public static void print() {
    System.out.println("This is printer");
  }

  static class Printer { }
}

After

public class Office {
  public static void main(String[] args) {
    Printer.print();
  }

  static class Printer {
    public static void print() {
      System.out.println("This is printer");
    }
  }
}

Rename

Default shortcut: F2

Renames the selected element and corrects all references to the elements (also in other files).

Examples

Let's rename the class Foo to Bar

Before

public class Foo {
  // ...
}

public void myMethod() {
  Foo myClass = new Foo();
}

After

public class Bar {
  // ...
}

public void myMethod() {
  Bar myClass = new Bar();
}

Change resolved type to var type

Uses var to declare local variables.

Examples

Before

String s = "";

After

var s = "";

Also see: Change var type to resolved type

Change var type to resolved type

Uses the resolved type to declare local variables.

Examples

Before

var s = "";

After

String s = "";

Also see: Change resolved type to var type