8-Map接口和常用方法 - ToB企服应用市场:ToB评测及商务社交产业平台

package map;
import java.lang.reflect.Field;
import java.util.HashMap;
public class MapEntrySet {
@SuppressWarnings({"all"})
public static void main(String[] args) {
HashMap hashMap = new HashMap();
Field entrySetField = null ;
try {
// 通过反射机制获取 HashMap 中的 entry 属性成员（Set<Map.Entry<K,V>> 类型）
entrySetField = HashMap.class.getDeclaredField("entrySet");
// 开启 entry 属性成员的访问权限
entrySetField.setAccessible(true);
// 从 HashMap 对象中获取 entry 属性成员
Object entrySet = entrySetField.get(hashMap);
// 打印该属性成员，查看属性成员是否为空
System.out.println("entrySet=" + entrySet);
// 模拟 IDEA 的 Debug 过程中调用 toString 方法获取数据（检验 entrySet 属性是否被初始化）
System.out.println("hashMap.toString" + hashMap.toString());
// 从 HashMap 对象中获取 entry 属性成员
entrySet = entrySetField.get(hashMap);
// 打印该属性成员，查看属性成员是否为空
System.out.println("entrySet=" + entrySet);
} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}
}

复制代码

package map;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class HashMapExercise {
@SuppressWarnings({"all"})
public static void main(String[] args) {
HashMap hashMap = new HashMap();
hashMap.put(1,new Employee02("吴彦祖",20000,1)) ;
hashMap.put(2,new Employee02("彭于晏",15000,2)) ;
hashMap.put(3,new Employee02("杨洋",28000,3)) ;
// Set<Map.Entry<K,V>> 遍历
Set entrySet = hashMap.entrySet();
Iterator iterator = entrySet.iterator();
while (iterator.hasNext()) {
Map.Entry entry = (Map.Entry) iterator.next();
Employee02 entryValue = (Employee02) entry.getValue();
if (entryValue.getSalary() > 18000) {
System.out.println("====工资大于 18000 的员工信息为" + entryValue);
}
}
// keySet 遍历
Set keySet = hashMap.keySet();
for (Object object : keySet) {
Employee02 employee02 = (Employee02) hashMap.get(object);
if (employee02.getSalary() >18000) {
System.out.println("====工资大于 18000 的员工信息为" + employee02);
}
}
}
}
@SuppressWarnings({"all"})
class Employee02 {
private String name ;
private double salary ;
private int id ;
@Override
public String toString() {
return "Employee02{" +
"name='" + name + '\'' +
", salary=" + salary +
", id=" + id +
'}';
}
public Employee02(String name, double salary, int id) {
this.name = name;
this.salary = salary;
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
}

复制代码