该方法的目的和目标是从
import java.util.HashMap;
import java.util.Map;
public class test {
public static void main(String[] args) {
reverse();
}
public Map<String, Integer> reverse(Map<Integer, String> map) {
HashMap<String, Integer> reversed = new HashMap<String, Integer>();
reversed.put("Eightenn", 18);
reversed.put("Fifty", 50);
reversed.put("neThreeTwo", 132);
reversed.put("Ocho", 8);
reversed.put("Forty-one", 41);
System.out.println("Reversered map " + reversed);
for(int key : map.keySet()) {
String value = map.get(key);
if(!reversed.containsKey(value)) {
reversed.put(value, key);
}
}
return reversed;
}
}
该方法的目的和目标是从
reverse()
方法需要 Map<Integer, String>
参数并返回一个 Map<Integer, String>
对象,但是您调用它时没有任何参数也没有分配对象。
我修改了你的代码,这应该可以。
import java.util.HashMap;
import java.util.Map;
public class test {
public static void main(String[] args) {
Map<Integer, String> original = new HashMap<Integer, String>();
original.put(18, "Eightenn");
original.put(50, "Fifty");
original.put(132, "neThreeTwo");
Map<String, Integer> reversed = reverse(original);
System.out.println("Reversed map: " + reversed);
}
public static Map<String, Integer> reverse(Map<Integer, String> map) {
Map<String, Integer> reversed = new HashMap<String, Integer>();
for(int key : map.keySet()) {
String value = map.get(key);
reversed.put(value, key);
}
return reversed;
}
}