How to use Pattern Matching for type pattern matching in Java 14

How to use Pattern Matching for type pattern matching in Java 14

Introduction:
Java 14 introduces a new feature, Pattern Matching, which is a powerful tool for Type pattern matching is performed at compile time. This article explains how to use Pattern Matching for type pattern matching in Java 14 and provides code examples.

1. Understand the concept of Pattern Matching
   Pattern Matching is a function that performs pattern matching based on the value and type of an expression at compile time. It greatly simplifies the process of writing conditional statements and provides more concise and readable code. In Java, Pattern Matching is implemented using the "instanceof" operator and the new "var" keyword.
2. Basic Usage
   In Java 14, you can use the "instanceof" operator and the new "var" keyword for type pattern matching. The following is a simple example:

public static void main(String[] args) {
    Object obj = "Hello, World";
    if (obj instanceof String str) {
        System.out.println("The object is of type String: " + str);
    } else {
        System.out.println("The object is not of type String");
    }
}

In this example, we first declare a variable "obj" of type Object, whose value is "Hello, World". We then use the "instanceof" operator to compare "obj" to a String and assign the result to a new variable "str" ​​of type String. If the match is successful, that is, the object is of type String, we can use the "str" ​​variable in the if statement block. Otherwise, we can execute the code of the else statement block.

3. Use switch statement for pattern matching
   In addition to if statement, we can also use switch statement for pattern matching. Here is an example using a switch statement:

public static void main(String[] args) {
    Object obj = "Hello, World";
    switch (obj) {
        case String str -> System.out.println("The object is of type String: " + str);
        case Integer integer -> System.out.println("The object is of type Integer: " + integer);
        default -> System.out.println("The object is not of type String or Integer");
    }
}

In this example, we perform pattern matching based on the type of object. If the object is of type String, we can use the "str" ​​variable in the case clause; if the object is of type Integer, we can use the "integer" variable in the case clause; otherwise, we can execute the code.

4. Further pattern matching examples
   In addition to basic type pattern matching, Pattern Matching can also be used with other language features to better handle complex situations. Here is a further example:

public static void main(String[] args) {
    Object obj = "Hello, World";
    if (obj instanceof String str && str.length() > 5) {
        System.out.println("The object is of type String with length greater than 5: " + str);
    } else if (obj instanceof Integer integer && integer > 10) {
        System.out.println("The object is of type Integer greater than 10: " + integer);
    } else {
        System.out.println("The object is not of the expected type or does not meet the condition");
    }
}

In this example, we first compare the object with String type and check if its length is greater than 5. If the match is successful, we can use the "str" ​​variable in the if statement block; otherwise, we continue to compare the object with the Integer type and check whether its value is greater than 10. If the match is successful, we can use the "integer" variable in the else if statement block. Finally, if none of the conditions are met, we can execute the code in the else statement block.

Conclusion:
Pattern Matching is a powerful feature introduced in Java 14 that can be used for type pattern matching at compile time. This article introduces the basic usage of Pattern Matching and provides code examples. By using Pattern Matching, we can write more concise and readable code, thereby improving the maintainability and scalability of the code. Therefore, it is recommended to take full advantage of Pattern Matching when using Java 14 and above.

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