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A magic number is a direct usage of a number in the code.

For example, if you have (in Java):

public class Foo { public void setPassword(String password) { // don't do this if (password.length() > 7) { throw new InvalidArgumentException("password"); } } } 

This should be refactored to:

public class Foo { public static final int MAX_PASSWORD_SIZE = 7; public void setPassword(String password) { if (password.length() > MAX_PASSWORD_SIZE) { throw new InvalidArgumentException("password"); } } } 

It improves readability of the code and it's easier to maintain. Imagine the case where I set the size of the password field in the GUI. If I use a magic number, whenever the max size changes, I have to change in two code locations. If I forget one, this will lead to inconsistencies.

The JDK is full of examples like in Integer, Character and Math classes.

PS.: Static analysis tools like FindBugs and PMD detects the use of magic numbers in your code and suggests the refactoring.

A magic number is a direct usage of a number in the code.

For example, if you have (in Java):

public class Foo { public void setPassword(String password) { // don't do this if (password.length() > 7) { throw new InvalidArgumentException("password"); } } } 

This should be refactored to:

public class Foo { public static final int MAX_PASSWORD_SIZE = 7; public void setPassword(String password) { if (password.length() > MAX_PASSWORD_SIZE) { throw new InvalidArgumentException("password"); } } } 

It improves readability of the code and it's easier to maintain. Imagine the case where I set the size of the password field in the GUI. If I use a magic number, whenever the max size changes, I have to change in two code locations. If I forget one, this will lead to inconsistencies.

The JDK is full of examples like in Integer, Character and Math classes.

PS: Static analysis tools like FindBugs and PMD detects the use of magic numbers in your code and suggests the refactoring.

A magic number is a direct usage of a number in the code.

public class Foo { public void setPassword(String password) { // don't do this if (password.length() > 7) { throw new InvalidArgumentException("password"); } } } 

This should be refactored to:

public class Foo { public static final int MAX_PASSWORD_SIZE = 7; public void setPassword(String password) { if (password.length() > MAX_PASSWORD_SIZE) { throw new InvalidArgumentException("password"); } } } 

It improves readability of the code and it's easier to maintain. Imagine the case where I set the size of the password field in the GUI. If I use a magic number, whenever the max size changes, I have to change in two code locations. If I forget one, this will lead to inconsistencies.

The JDK is full of examples like in Integer, Character and Math classes.

PS.: Static analysis tools like FindBugs and PMD detects the use of magic numbers in your code and suggests the refactoring.

A magic number is a direct usage of a number in the code.

For example, if you have (in Java):

public class Foo { public void setPassword(String password) { // don't do this if (password.length() > 7) { throw new InvalidArgumentException("password"); } } } 

This should be refactored to:

public class Foo { public static final int MAX_PASSWORD_SIZE = 7; public void setPassword(String password) { if (password.length() > MAX_PASSWORD_SIZE) { throw new InvalidArgumentException("password"); } } } 

It improves readability of the code and it's easier to maintain. Imagine the case where I set the size of the password field in the GUI. If I use a magic number, whenever the max size changes, I have to change in two code locations. If I forget one, this will lead to inconsistencies.

The JDK is full of examples like in Integer, Character and Math classes.

PS.: Static analysis tools like FindBugs and PMD detects the use of magic numbers in your code and suggests the refactoring.

A magic number is a direct usage of a number in the code.

public class Foo {   public void setPassword(String password) {   // don't do this   if (password.length() > 7) {   throw new InvalidArgumentException("password");   } } 

This should be refactored to:

public class Foo {   public static final int MAX_PASSWORD_SIZE = 7;   public void setPassword(String password) {   if (password.length() > MAX_PASSWORD_SIZE) {   throw new InvalidArgumentException("password");   } } 

It improves readability of the code and it's easier to maintain. Imagine the case where I set the size of the password field in the GUI. If I use a magic number, whenever the max size changes, I have to change in two code locations. If I forget one, this will lead to inconsistencies.

The JDK is full of examples like in Integer, Character and Math classes.

PS.: Static analysis tools like FindBugs and PMD detects the use of magic numbers in your code and suggests the refactoring.

A magic number is a direct usage of a number in the code.

public class Foo { public void setPassword(String password) { // don't do this if (password.length() > 7) { throw new InvalidArgumentException("password"); }  } } 

This should be refactored to:

public class Foo { public static final int MAX_PASSWORD_SIZE = 7; public void setPassword(String password) { if (password.length() > MAX_PASSWORD_SIZE) { throw new InvalidArgumentException("password"); }  } } 

It improves readability of the code and it's easier to maintain. Imagine the case where I set the size of the password field in the GUI. If I use a magic number, whenever the max size changes, I have to change in two code locations. If I forget one, this will lead to inconsistencies.

The JDK is full of examples like in Integer, Character and Math classes.

PS.: Static analysis tools like FindBugs and PMD detects the use of magic numbers in your code and suggests the refactoring.