Advanced Debugging Techniques in IntelliJ IDEA for Java Developers

IntelliJ IDEA, developed by JetBrains, is a widely used Java IDE that also supports Kotlin, Scala, Groovy, and Android development, offering powerful debugging capabilities essential for building stable software.

The article explains two advanced debugging techniques: conditional breakpoints, which pause execution only when a specified condition is met, and the Evaluate Expression (calculator) feature, which allows on‑the‑fly evaluation and modification of variables.

It provides a concrete example using a List<User> where the third element has a null age, causing a NullPointerException during arithmetic. The full source code is shown below:

/**
 * @author Liutx
 * @since 2023-12-04 14:09
 */
public class IDEATest {
    public static void main(String[] args) {
        List
userList = new ArrayList<>(6);
        userList.add(new User(1, "Tom", 19));
        userList.add(new User(2, "Giles", 25));
        userList.add(new User(3, "Alex", null));
        userList.add(new User(4, "Ryan", 21));
        userList.add(new User(5, "DongGe", 19));
        userList.add(new User(6, "RUI", 21));
        userList.forEach(user -> {
            String name = user.getName();
            int futureAge = user.getAge() + 10;
            System.out.println(name + " 10年后" + futureAge + "岁");
        });
    }
}

@Data
@AllArgsConstructor
@NoArgsConstructor
class User {
    private Integer id;
    private String name;
    private Integer age;
}

When debugging, a breakpoint is set on the line that adds 10 to user.getAge() . The condition Objects.isNull(user.getAge()) is added so the debugger stops only for the user with a null age, instantly revealing the problematic entry.

The article also describes how the Evaluate Expression tool can be used to view or modify variable values, test expressions, and even invoke methods without restarting the debugging session, greatly speeding up troubleshooting.

Finally, it notes that conditional breakpoints are useful when reading source code of frameworks such as Spring, allowing developers to pinpoint specific bean loading logic during runtime.