How can Java determine if an object exists?

In Java, the null keyword can be used to determine if an object exists. When an object does not exist, its value is null. The == or != operators can be used to check if an object is null.

For example:

String str = "Hello";
if (str != null) {
    // 对象存在的处理逻辑
    System.out.println("对象存在");
} else {
    // 对象不存在的处理逻辑
    System.out.println("对象不存在");
}

Furthermore, you can also use the Objects.isNull() method (available in Java 8 and above) to determine if an object is null.

import java.util.Objects;

String str = "Hello";
if (Objects.isNull(str)) {
    // 对象不存在
    System.out.println("对象不存在");
} else {
    // 对象存在
    System.out.println("对象存在");
}

This approach can avoid using the == or != operators for comparison, improving the readability of the code.