replaceAll 是 java.util.Map 的默认方法，已在 Java 8 中引入。replaceAll 方法接受 BiFunction 作为参数。 replaceAll 方法将每个条目值Replace为对该条目调用给定函数的结果。 replaceAll 适用于 Map 的每个条目，或者如果指定函数对任何条目抛出异常，它就会停止。从 Java 文档中找到方法声明。

default void replaceAll(BiFunction<? super K,? super V,? extends V> function)

我们需要传递将应用于 Map 的每个条目的 BiFunction。

示例-1

在此示例中，我们使用的是 HashMap。
ReplaceAll1.java

import java.util.HashMap;
import java.util.Map;

public class ReplaceAll1 {
  public static void main(String[] args) {
     Map<Integer, String> studentMap = new HashMap<>();
     studentMap.put(101, "Mahesh");
     studentMap.put(102, "Suresh");
     studentMap.put(103, "Krishna");
     
     System.out.println("--- before replaceAll() ---");
     
     System.out.println(studentMap);
     
     studentMap.replaceAll((k,v) -> v + "-" + k);
     
     System.out.println("--- after replaceAll() ---");
     
     System.out.println(studentMap);     
  }
}

输出

--- before replaceAll() ---
{101=Mahesh, 102=Suresh, 103=Krishna}
--- after replaceAll() ---
{101=Mahesh-101, 102=Suresh-102, 103=Krishna-103}

同样可以通过使用 Map.Entry 迭代 Map 来实现。
MapEntryTest.java

import java.util.HashMap;
import java.util.Map;
import java.util.function.BiFunction;

public class MapEntryTest {
  public static void main(String[] args) {
     Map<Integer, String> studentMap = new HashMap<>();
     studentMap.put(101, "Mahesh");
     studentMap.put(102, "Suresh");
     studentMap.put(103, "Krishna");
     
     System.out.println("--- before replaceAll() ---");
     
     System.out.println(studentMap);
     
     BiFunction<Integer, String, String> function = (k, v) -> v + "-" + k;
     
     for (Map.Entry<Integer, String> entry : studentMap.entrySet())
       entry.setValue(function.apply(entry.getKey(), entry.getValue()));
     
     System.out.println("--- after replaceAll() ---");
     
     System.out.println(studentMap);     
  }
}

输出

--- before replaceAll() ---
{101=Mahesh, 102=Suresh, 103=Krishna}
--- after replaceAll() ---
{101=Mahesh-101, 102=Suresh-102, 103=Krishna-103}

示例-2

再找一个使用 HashMap 的例子。
ReplaceAll2.java

import java.util.HashMap;
import java.util.Map;

public class ReplaceAll2 {
  public static void main(String[] args) {
     Map<Integer, String> studentMap = new HashMap<>();
     studentMap.put(101, "Mahesh");
     studentMap.put(102, "Suresh");
     studentMap.put(103, "Krishna");
     
     System.out.println("--- before replaceAll() ---");
     
     System.out.println(studentMap);
     
     studentMap.replaceAll((k,v) -> {
       if (k == 102) {
         return v + "-" + k;
       }
       return v;
     });
     
     System.out.println("--- after replaceAll() ---");
     
     System.out.println(studentMap);     
  }
}

输出

--- before replaceAll() ---
{101=Mahesh, 102=Suresh, 103=Krishna}
--- after replaceAll() ---
{101=Mahesh, 102=Suresh-102, 103=Krishna}

示例-3

在此示例中，我们使用的是 LinkedHashMap。
ReplaceAll3.java

import java.util.LinkedHashMap;
import java.util.Map;

public class ReplaceAll3 {
  public static void main(String[] args) {
     Map<Integer, Integer> numberMap = new LinkedHashMap<>();
     numberMap.put(1, 100);
     numberMap.put(2, 200);
     numberMap.put(3, 300);
     
     System.out.println("--- before replaceAll() ---");
     
     System.out.println(numberMap);
     
     numberMap.replaceAll((k, v) -> v * k);
     
     System.out.println("--- after replaceAll() ---");
     
     System.out.println(numberMap);
  }
}

输出

--- before replaceAll() ---
{1=100, 2=200, 3=300}
--- after replaceAll() ---
{1=100, 2=400, 3=900}

示例-4

在此示例中，我们使用的是 TreeMap。
ReplaceAll4.java

import java.util.Map;
import java.util.TreeMap;

public class ReplaceAll4 {
  public static void main(String[] args) {
     Map<String, String> treeMap = new TreeMap<>();
     treeMap.put("Bharat", "Modi");
     treeMap.put("Russia", "Putin");
     treeMap.put("USA", "Trump");
     
     System.out.println("--- before replaceAll() ---");
     System.out.println(treeMap);
     
     treeMap.replaceAll((k, v) -> "Mr. "+ v);
     
     System.out.println("--- after replaceAll() ---");
     System.out.println(treeMap);
  }
}

输出

--- before replaceAll() ---
{Bharat=Modi, Russia=Putin, USA=Trump}
--- after replaceAll() ---
{Bharat=Mr. Modi, Russia=Mr. Putin, USA=Mr. Trump}