Extract/Introduce variable

If you come across an expression that is hard to understand or it is duplicated in several places throughout your code, the Extract Variable refactoring CtrlAlt0V can help you deal with those problems placing the result of such expression or its part into a separate variable that is less complex and easier to understand. Plus, it reduces the code duplication.

Starting with Java 1.8 and later versions, IntelliJ IDEA also lets you extract a functional type variable.

If your Java version supports the pattern matching (Java 14 preview or higher) and you are extracting a cast expression under the instanceof check, IntelliJ IDEA may introduce a pattern variable at that instanceof check instead of a normal local variable. Also, you can inline pattern variable since the Java 14 version. In this case, all the occurrences will be replaced with old-style cast expression.

You can use the Introduce Variable refactoring to extract variadic arguments into a new slice variable.

tip

By default, this extract refactoring will be applied in the editor. To change your settings to apply the refactoring via a modal open the Settings dialog (CtrlAlt0S) , go to Editor | Code Editing, and in the Refactorings area select In modal dialogs.

public void method() {
    int a = 1;
...
    int b = a + anotherClass.intValue();
    int c = b + anotherClass.intValue();
}

public void method() {
    int a = 1;
...
    int number = anotherClass.intValue();
    int b = a + number;
    int c = b + number;
}

func method() {
     val a = 1
     val b = a + anotherClass!!.intValue()
     val c = b + anotherClass!!.intValue()
}

func method() {
     val a = 1
     val number = anotherClass!!.intValue()
     val b = a + number
     val c = b + number
}

import java.util.List;

public class PrintAction implements Runnable {
    private List<String> data;

    public PrintAction(List<String> data) {
        this.data = data;
    }

    public void run() {
        System.out.println("Data: " + data.toString());
    }
}

import java.util.List;
import java.util.function.Function;

public class PrintAction implements Runnable {
    private List<String> data;

    public PrintAction(List<String> data) {
        this.data = data;
    }

    public void run() {
        Function<List<String>, String> presenter = (p) -> "Data: " + p.toString();
        System.out.println(presenter.apply(data));
    }
}