Properties类的computeIfPresent(Key,BiFunction)方法,如果key已经与某个值关联(或映射为null),则可以使用该方法为指定的key计算映射值。
- 如果此方法的映射函数返回null,则将删除该映射。
- 如果重新映射函数引发异常,则重新引发该异常,并且映射保持不变。
- 在计算过程中,不允许使用此方法修改此Map。
- 如果重新映射函数在计算过程中修改了此映射,则此方法将引发ConcurrentModificationException。
用法:
public Object computeIfPresent?(Object key, BiFunction remappingFunction)
参数:此方法接受两个参数:
- key与值关联的:key。
- remappingFunction:function对值进行运算。
返回值:此方法返回与指定键关联的新的重新映射的值;如果映射返回null,则返回null。
异常:如果检测到重新映射函数修改了此映射,则此方法将引发ConcurrentModificationException。
以下示例程序旨在说明computeIfPresent(Key,BiFunction)方法:
程序1:
// Java program to demonstrate
// computeIfPresent(Key, BiFunction) method.
import java.util.*;
public class GFG {
// Main method
public static void main(String[] args)
{
// Create a properties and add some values
Properties properties = new Properties();
properties.put("Pen", 10);
properties.put("Book", 500);
properties.put("Clothes", 400);
properties.put("Mobile", 5000);
// print Properties details
System.out.println("Current Properties:"
+ properties.toString());
// provide new value for keys which is present
// using computeIfPresent method
properties.computeIfPresent("Pen", (key, val)
-> 600);
properties.computeIfPresent("Book", (key, val)
-> 800);
// print new mapping
System.out.println("New Properties:"
+ properties.toString());
}
}
输出:
Current Properties:{Book=500, Mobile=5000, Pen=10, Clothes=400} New Properties:{Book=800, Mobile=5000, Pen=600, Clothes=400}
程序2:
// Java program to demonstrate
// computeIfPresent(Key, BiFunction) method.
import java.util.*;
public class GFG {
// Main method
public static void main(String[] args)
{
// Create a properties and add some values
Properties properties = new Properties();
properties.put(1, "100RS");
properties.put(2, "500RS");
properties.put(3, "1000RS");
// print Properties details
System.out.println("Current Properties:"
+ properties.toString());
// provide new value for key which is present
// using computeIfPresent method
properties.computeIfPresent(3, (key, val)
-> "00RS");
// this will not effect anything
// because key 4 is absent
properties.computeIfPresent(4, (key, val)
-> "$");
// print new mapping
System.out.println("New Properties:"
+ properties.toString());
}
}
输出:
Current Properties:{3=1000RS, 2=500RS, 1=100RS} New Properties:{3=00RS, 2=500RS, 1=100RS}
参考:https://docs.oracle.com/javase/9/docs/api/java/util/Properties.html#computeIfPresent-java.lang.Object-java.util.function.BiFunction-
相关用法
- Java Properties compute(Key, BiFunction)用法及代码示例
- Java HashMap merge(key, value, BiFunction)用法及代码示例
- Java HashMap replaceAll(BiFunction)用法及代码示例
- Java HashMap computeIfPresent(key, BiFunction)用法及代码示例
- Java Properties get(key)用法及代码示例
- Java Properties contains(value)用法及代码示例
- Java Properties keySet()用法及代码示例
- Java Properties equals(value)用法及代码示例
- Java Properties elements()用法及代码示例
- Java Properties keys()用法及代码示例
- Java Properties clear()用法及代码示例
- Java Properties containsValue(value)用法及代码示例
- Java Properties containsKey(value)用法及代码示例
- Java Properties entrySet()用法及代码示例
- Java Properties getProperty(key)用法及代码示例
注:本文由纯净天空筛选整理自Kirti_Mangal大神的英文原创作品 Properties computeIfPresent(Key, BiFunction) method in Java with Examples。非经特殊声明,原始代码版权归原作者所有,本译文未经允许或授权,请勿转载或复制。