Application method of common class and tools in the Core framework in the Java class library
Application method of common class and tools in the Core framework in the Java class library
In Java programming, the Java class library is a very important resource. It contains many core framework categories and tools, which can help us develop and solve problems more efficiently.This article will introduce some of the commonly used classes and tools in the Java library and provide related examples.
1. Object class:
Object class is a parent class in Java, which provides many common methods, such as Equals () to compare whether the two objects are equal, the hashcode () for the hash code used to obtain the object, tostring () is used to obtain to obtainThe string of the object, etc.The following is a simple example of the Object class:
public class Person {
private String name;
private int age;
// Construction method, Getter and Setter omitted
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null || getClass() != obj.getClass()) {
return false;
}
Person person = (Person) obj;
return age == person.age && Objects.equals(name, person.name);
}
@Override
public int hashCode() {
return Objects.hash(name, age);
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}
2. String class:
The String class is a string commonly used in Java. It provides many methods for operating string, such as length () to obtain the length of the string, char () is used to obtain characters on the specified index position.Find the location where the character or string appears for the first time.The following is an example of the String class:
String str = "Hello, World!";
System.out.println (str.length ()); // Output: 13
System.out.println (str.charat (7)); // Output: w
System.out.println (str.indexof ("o"); // Output: 4
3. Math class:
The Math class provides many mathematical -related methods, such as ABS () to obtain absolute values, POW () is used to calculate the exponential power, SQRT () is used to find the flat root root.The following is an example of the Math class:
double num1 = -10.5;
double num2 = 8.2;
System.out.println (math.abs (num1)); // Output: 10.5
System.out.println (math.pow (num2, 3)); // Output: 566.9880000000001
System.out.println (math.sqrt (num2)); // Output: 2.863564211151984
4. Date class:
The Date class is used to indicate the date and time. It provides some methods of operation date and time, such as Gettime () to obtain the milliseconds of the date, and) string representation used to obtain the date.The following is a simple example of the date class:
Date now = new Date();
System.out.println (now.gettime ()); // Output: 1635907033673
System.out.println (now.tostring ()); // Output: fri nov 05 18:10:33 gmt+08: 00 2021
5. Collections class:
The Collections class provides some commonly used collection operation methods, such as sort () to sort the list, reverse () is used to reverse the list, shuffle () is used to randomly disrupt lists.The following is an example of the Collections class:
List<Integer> numbers = new ArrayList<>(List.of(3, 1, 4, 1, 5, 9, 2, 6));
Collections.sort(numbers);
System.out.println (numbers); // Output: [1, 1, 2, 3, 4, 5, 6, 9]
Collections.shuffle(numbers);
System.out.println (numbers); // Output: List after random sorting
By mastering the application methods of common classes and tools in the Core framework in the Java class library, we can better use these classes and tools to accelerate the development process and solve some common programming problems.I hope this article will be helpful to your learning.
