String.format

"I also want to tell you about the String.format method."

"It's a static method of the String class, but it is very useful. Let me take a roundabout approach."

"If you need to display several variables on one line of text, how would you do it?"

"What text?"

"This, for example:"

String name = "Bender";
int age = 12;
String friend = "Fry";
int weight = 200;

User = {name: Bender, age: 12 years, friend: Fry, weight: 200 kg.}

"I'd do it something like this:"

String name = "Bender";
int age = 12;
String friend = "Fry";
int weight = 200;

System.out.println("User = {name: " + name + ", age: " + age + " years, friend: " + friend + ", weight: " + weight + " kg.}");

"Not very readable, is it?"

"I think it's okay."

"But if you have long variable names or you need to call methods to get data, then it wouldn't be very readable:"

System.out.println("User = {name: " + user.getName() + ", age: " + user.getAge() + " years, friend: " + user.getFriends().get(0) + ", weight: " + user.getExtraInformation().getWeight() + " kg.}");

"Well, if that were the case, then, yes, it wouldn't be very readable."

"The fact is this happens all the time in real programs, so I want to show you how you can simplify your life with the String.format method."

"Please tell me quickly, what kind of magical method is this?"

"You can write the code above like this:"

String text = String.format("User = {name: %s, age: %d years, friend: %s, weight: %d kg.}",
user.getName(), user.getAge(), user.getFriends().get(0), user.getExtraInformation().getWeight())

System.out.println(text);

"The String.format method's first parameter is a format string that contains special characters (%s, %d) wherever we want to put values."

"After the format string, we pass the values that will replace the %s and %d characters."

"If we need to insert a string, then we write %s; if we need a number, then we use %d."

"It will be easier to see this in an example:"

String s = String.format("a = %d, b = %d, c = %d", 1, 4, 3);

s will be equal to «a = 1, b = 4, c = 3»

"Yeah, that's very convenient."

"And you can also do it like this:"

int a = -1, b = 4, c = 3;
String template;
 if (a < 0)
  template = "Warning! a = %d, b = %d, c = %d";
 else
  template = "a = %d, b = %d, c = %d";

System.out.println(String.format(template, a, b, c) );

Warning! a = -1, b = 4, c = 3

"Hmm. That is a really useful method. Thanks, Ellie."

"If you want to use other data types with the format method, here's a table that will help:"

"Actually, these format specifiers also have their own settings and subsettings."

"But this is enough to get you started. If not, here's a link to the official documentation:"

Link to additional material