Java 中的 TimeUnit valueOf()方法，示例

原文:https://www . geesforgeks . org/time unit-value of-method-in-Java-with-examples/

时间单位类的 valueOf() 方法返回指定名称的该类型枚举常量。该字符串必须与用于声明此类型的枚举常量的标识符完全匹配。(不允许使用额外的空白字符。)

语法:

public static TimeUnit valueOf(String name)

参数:这个方法接受一个强制参数名称，这是要返回的枚举常量的名称。

返回值:该方法返回指定名称的枚举常量

异常:该方法抛出以下异常:

  • IllegalArgumentException–如果此枚举类型没有具有指定名称的常量
  • 空指针异常–如果参数为空

下面的程序说明了 TimeUnit valueOf()方法的实现:

程序 1:

// Java program to demonstrate
// valueOf() method of TimeUnit Class

import java.util.concurrent.*;

class GFG {
    public static void main(String args[])
    {

        // Create an object of TimeUnit class
        // using valueOf() method
        // Below statement is equivalent to
        // TimeUnit Days = TimeUnit.DAYS;
        TimeUnit Days = TimeUnit.valueOf("DAYS");

        // Print the Enum of TimeUnit Object
        System.out.println("TimeUnit object "
                           + "is of type: "
                           + Days);

        // Convert current object to Hours
        System.out.println("1 Day = "
                           + Days.toHours(1)
                           + " Hours");
    }
}

Output:

TimeUnit object is of type: DAYS
1 Day = 24 Hours

程序 2: 演示空指针异常

// Java program to demonstrate
// valueOf() method of TimeUnit Class

import java.util.concurrent.*;

class GFG {
    public static void main(String args[])
    {

        try {

            System.out.println("Trying to create "
                               + "TimeUnit object "
                               + "using null Enum type");

            // Create an object of TimeUnit class
            // using valueOf() method
            // by passing null as parameter
            TimeUnit Days = TimeUnit.valueOf(null);
        }

        catch (NullPointerException e) {
            System.out.println("\nException thrown: " + e);
        }
    }
}

Output:

Trying to create TimeUnit object using null Enum type

Exception thrown: java.lang.NullPointerException: Name is null

程序 3: 演示 IllegalArgumentException

// Java program to demonstrate
// valueOf() method of TimeUnit Class

import java.util.concurrent.*;

class GFG {
    public static void main(String args[])
    {

        try {

            System.out.println("Trying to create "
                               + "TimeUnit object "
                               + "using ABCD Enum type");

            // Create an object of TimeUnit class
            // using valueOf() method
            // by passing ABCD as parameter
            TimeUnit Days = TimeUnit.valueOf("ABCD");
        }

        catch (IllegalArgumentException e) {
            System.out.println("\nException thrown: " + e);
        }
    }
}

Output:

Trying to create TimeUnit object using ABCD Enum type

Exception thrown: java.lang.IllegalArgumentException: No enum constant java.util.concurrent.TimeUnit.ABCD

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