属性计算 Java 中的 Present(Key，BiFunction)方法，示例
属性类的计算当前(键，双功能)方法，如果键已经与值相关联(或映射为空)，则允许您计算指定键的映射值。
- If the mapping function of this method returns null, the mapping is removed.
- If the remapping function throws an exception, it throws an exception again, and the mapping remains unchanged.
- This method is not allowed to modify the map during the calculation.
- If the remapping function modifies this mapping during calculation, this method will throw a Concurrentmodification Exception.
语法:
public Object computeIfPresent?(Object key,
BiFunction remappingFunction)
参数:此方法接受两个参数:
- key : the key with which the value is to be associated.
- [T0】 remapingfunction 【T1]: the function of computing numerical values.
返回:该方法返回与指定键关联的新的重映射值，如果映射返回空值，则返回空值。
异常:如果检测到重映射函数修改了该地图，则该方法抛出ConcurrentModificationException。
下面的程序说明了计算呈现(键，双功能)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}
程序二:
// 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)
-> "{content}quot;);
// 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}
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