What are predefined methods in Java library?
What are predefined methods in Java library?
I'm happy to help you with that! In the Java library, there are several predefined methods that can be used directly without having to write custom code. These methods are part of various classes and interfaces that are available out of the box.
One such example is the String class, which provides a number of overloaded methods for manipulating strings. For instance:
toLowerCase(): Returns a string with all uppercase characters converted to lowercase. toUpperCase(): Returns a string with all lowercase characters converted to uppercase. trim(): Removes leading and trailing whitespace from a string. substring(int start): Returns a new string that is a subset of the original string, starting at the specified index. concat(String str): Appends one or more strings together.
Another example is the Math class, which provides methods for performing mathematical operations. Some examples include:
abs(double d): Returns the absolute value of a number. ceil(double d): Returns the smallest integer that is greater than or equal to the specified double value. floor(double d): Returns the largest integer that is less than or equal to the specified double value. max(double a, double b): Returns the larger of two values.
The Date and Calendar classes in the Java library also provide a number of methods for working with dates. Some examples include:
getTime(): Returns the time represented by this date, measured in milliseconds from the epoch (January 1, 1970, 00:00:00 GMT). getHours(): Returns the hour of the day (0-23) as if it were daytime. add(int field, int amount): Adds a specified amount to a specified field in this Calendar.
The List, Set, and Map interfaces in the Java library provide methods for manipulating collections. For instance:
clear(): Removes all elements from this collection (optional operation). isEmpty(): Returns true if this collection contains zero elements. contains(Object o): Returns true if this collection contains one or more matching elements.
These are just a few examples of the many predefined methods available in the Java library. These methods can be very useful when working with strings, numbers, dates, and collections, as they provide a way to perform common operations without having to write custom code.
What is an example of a pre-defined method in Java?
I'm happy to help you with your question!
In Java, a pre-defined method refers to a built-in method that is part of the Java language itself. These methods are implemented by the JVM (Java Virtual Machine) and provide basic functionality for performing various tasks.
One example of a pre-defined method in Java is toString(). This method is used to convert an object into a string representation. When you call toString() on an object, it returns a string that represents the object's state or content. For instance:
public class Person {private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + ''' +
", age=" + age +
'}';
}
}
When you create a Person object and call its toString() method, it will return a string like this:
public static void main(String[] args) {Person person = new Person("John", 30);
System.out.println(person.toString()); // Output: Person{name='John', age=30}
}
Another example of a pre-defined method in Java is equals(). This method compares two objects for equality. When you override the equals() method in your own class, it should follow specific guidelines to ensure correct comparison behavior.
Here's an example:
public class Person {private String name;
public Person(String name) {
this.name = name;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (!(obj instanceof Person))
return false;
Person person = (Person) obj;
return this.name.equals(person.getName());
}
}
When you call equals() on two Person objects, it will compare their name fields for equality.
These are just a few examples of pre-defined methods in Java. There are many more built-in methods that provide useful functionality for developers to use and extend.
I hope this helps clarify things! Let me know if you have any further questions.
