JAVA第七章集合（四）

Map接口

Map与Collection 是并列在，用保存具有映射关系的数据：key-Value Map中的key和value都可以是任何类型的数据 Map中的key用Set来存放，不允许重复，既同一个Map对象所对应的类。须重写hashCode()和equals（）方法 常用String类作为Map的“键”。 key和value之间存在单向的一对一关系。既通过指定的key总能找到唯一的确定的value

HashMap

1.key是用Set来存放的，不可重复，value是用Collection来存放的。可重复，一个key-value对是一个Entry所有的Entry是用Set存放的也是不可重复的。 2.向HashMap中添加元素时。会调用key所在类的equals（）方法，判断俩个key是否相同，若相同则只能添加进后加的那个元素 Map接口 |…HashMap(主要实现类） |…LinkedHashMap； |…TreeMap |…Hashtable |….Properties; Map常用的方法 添加，删除操作 Object put(Object key,Object value)向Map中添加一个元素 Object remove(Object key)按照指定的key删除此key-value void putAll(Map t) void clear()：清空

元素查询的操作 Object get(Object key)获取指定key的value值 若无此key则返回null boolean containsKey(Object key) boolean containsValue(Object value) int size()返回集合的长度 boolean isEmpty() boolean equlas(Object obj) 元视图操作的方法 Set keySet() Collection values() Set entrySet()

package Collection; public class Person implements Comparable { private String name; private Integer id; public Person() { super(); } public Person(String name, Integer id) { super(); this.name = name; this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((id == null) ? 0 : id.hashCode()); result = prime * result + ((name == null) ? 0 : name.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Person other = (Person) obj; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other.id)) return false; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; return true; } @Override public String toString() { return "Person [name=" + name + ", id=" + id + "]"; } @Override public int compareTo(Object o) { if(o instanceof Person){ Person p=(Person)o; int i=this.id.compareTo(p.id); if(i==0){ return this.name.compareTo(p.name); }else{ return i; } } return 0; } } package Collection; import java.util.Collection; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Set; import org.junit.Test; public class testHashMap { @Test public void testOne(){ Map map= new HashMap(); Map map1= new HashMap(); map1.put("AA", 123); map1.put("BB", 235); map1.put("SS", 1235); map.put("AA", 123); map.put("BB", 235); map.put("SS", 1235); map.put("VV", 224); map.put("AA", 456); map.put(123, new Person("AA",123)); map.put(new Person("BB",124), 124); map.put(new Person("BB",124), 125); System.out.println(map.size()); //map.remove("AA"); //System.out.println(map.size()); //map.clear(); //System.out.println(map.size()); System.out.println(map.get("AA")); System.out.println(map.get(444)); System.out.println(map.get("AA").equals(map.get("BB")));//比较俩个是否相等 System.out.println(map.isEmpty());//判断是否为空 boolean b1=map.containsValue(224);//判断map中是否包含该values值 boolean b2=map.containsKey("AA");//判断改制中是否包含其key System.out.println(b1); System.out.println(b2); //进行遍历 Set set=map.keySet();//遍历key for(Object obj:set){ System.out.println(obj); } Collection com=map.values(); Iterator i=com.iterator();//遍历values while(i.hasNext()){ System.out.println(i.next()); } Set set1=map.keySet(); for(Object obj:set1){ System.out.println(obj+"----------------->"+map.get(obj)); }//entrySet方式一 Set ste2=map.entrySet(); for(Object obj:ste2){ Map.Entry entry=(Map.Entry)obj; System.out.println(entry.getKey()+"--------->"+entry.getValue()); }//方式二 Set ste3=map.entrySet(); for(Object obj:ste3){ Map.Entry entry=(Map.Entry)obj; System.out.println(entry); } } } 运行结果 6 456 null false false true true AA BB SS VV Person [name=BB, id=124] 123 456 235 1235 224 125 Person [name=AA, id=123] AA----------------->456 BB----------------->235 SS----------------->1235 VV----------------->224 Person [name=BB, id=124]----------------->125 123----------------->Person [name=AA, id=123] AA--------->456 BB--------->235 SS--------->1235 VV--------->224 Person [name=BB, id=124]--------->125 123--------->Person [name=AA, id=123] AA=456 BB=235 SS=1235 VV=224 Person [name=BB, id=124]=125 123=Person [name=AA, id=123]

LinkedHashMap

使用链表维护添加进Map中的顺序，故遍历Map是按照添加的顺序遍历的

package Collection; import java.util.Collection; import java.util.HashMap; import java.util.Iterator; import java.util.LinkedHashMap; import java.util.Map; import java.util.Set; import org.junit.Test; public class testHashMap { @Test public void tetsTwo(){ Map map= new LinkedHashMap(); map.put("BB", 235); map.put("SS", 1235); map.put("VV", 224); map.put("AA", 456); map.put(123, new Person("AA",123)); map.put(new Person("BB",124), 124); map.put(new Person("BB",124), 125); Set ste2=map.entrySet(); for(Object obj:ste2){ Map.Entry entry=(Map.Entry)obj; System.out.println(entry.getKey()+"--------->"+entry.getValue()); } } } 运行结果 BB--------->235 SS--------->1235 VV--------->224 AA--------->456 123--------->Person [name=AA, id=123] Person [name=BB, id=124]--------->125

TreeMap方法

//自排序 @Test//自排序 public void tetsOne(){ Map map=new TreeMap(); map.put(new Person("AA",124), 110); map.put(new Person("CC",125), 132); map.put(new Person("TT",126), 98); map.put(new Person("VV",123), 214); map.put(new Person("EE",152), 20); map.put(new Person("AA",142), 24); Set ste2=map.entrySet(); for(Object obj:ste2){ Map.Entry entry=(Map.Entry)obj; System.out.println(entry.getKey()+"--------->"+entry.getValue()); } } 运行结果 Person [name=VV, id=123]--------->214 Person [name=AA, id=124]--------->110 Person [name=CC, id=125]--------->132 Person [name=TT, id=126]--------->98 Person [name=AA, id=142]--------->24 Person [name=EE, id=152]--------->20 //定制排序 ackage Collection; public class Customer { private String name; private Integer id; public Customer() { super(); } public Customer(String name, Integer id) { super(); this.name = name; this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } @Override public String toString() { return "Customer [name=" + name + ", id=" + id + "]"; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((id == null) ? 0 : id.hashCode()); result = prime * result + ((name == null) ? 0 : name.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Customer other = (Customer) obj; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other.id)) return false; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; return true; } } package Collection; import java.util.Comparator; import java.util.Map; import java.util.Set; import java.util.TreeMap; import org.junit.Test; public class testTreeMaop { @Test public void testTwo(){ Comparator com= new Comparator(){ @Override public int compare(Object o1, Object o2) { if(o1 instanceof Customer && o2 instanceof Customer){ Customer c1=(Customer)o1; Customer c2=(Customer)o2; int i=c1.getId().compareTo(c2.getId()); if(i==0){ return c1.getName().compareTo(c2.getName()); }else{ return i; } } return 0; } }; Map map=new TreeMap(com); map.put( new Customer("AA",124),124); map.put( new Customer("SS",123),125); map.put( new Customer("GG",126),245); map.put( new Customer("mm",195),745); map.put( new Customer("ss",45),245); Set ste2=map.entrySet(); for(Object obj:ste2){ Map.Entry entry=(Map.Entry)obj; System.out.println(entry.getKey()+"--------->"+entry.getValue()); } } //运行结果 Customer [name=ss, id=45]--------->245 Customer [name=SS, id=123]--------->125 Customer [name=AA, id=124]--------->124 Customer [name=GG, id=126]--------->245 Customer [name=mm, id=195]--------->745

Hashtable

:古老的实现类，线程安全，不建议使用 Properties：常用来处理属性文件：键和值都是String类型的。

使用Properties处理属性文件 package Collection; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.util.Comparator; import java.util.Map; import java.util.Properties; import java.util.Set; import java.util.TreeMap; import org.junit.Test; public class testTreeMaop { @Test public void Three() throws FileNotFoundException, IOException{ Properties pros=new Properties(); pros.load(new FileInputStream(new File("jdbc.properties")) ); String user=pros.getProperty("user"); String password=pros.getProperty("password"); System.out.println("uesr"+"="+user+"\n"+"password"+password); } 文件内容 user=root password=123abc 运行结果 uesr=root password123abc