集合02/Collection常用方法1

た入场券 2023-10-04 16:48 28阅读 0赞

#### Collection常用方法1 ####

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![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 1]

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#### 一、 ####

package com.mjl;
    
    import org.junit.Test;
    
    import java.util.ArrayList;
    import java.util.Collection;
    import java.util.Date;
    
    public class CollectionTest  {
        
    
        @Test
        public void test() {
        
            Collection coll = new ArrayList();
    
            //add(Object):将元素e添加到集合coLl中
            coll.add("AA");
            coll.add("BB");
            coll.add(123);
            coll.add(new Date());
    
            //size():获取添加的元素的个数
            System.out.println(coll.size());//4
    
            //addAll(Collection coll1):将coll1集合中的元素添加到当前的集合中
            Collection coll1 = new ArrayList();
            coll1.add(456);
            coll1.add("CC");
            coll.addAll(coll1);
    
            System.out.println(coll.size());//6
            System.out.println(coll);
    
            //isEmpty():判断当前集合是否为空
            System.out.println(coll.isEmpty());//false
    
            //clear():清空集合元素。但是对象依然在，并不是吧coll赋值为null
            coll.clear();
            System.out.println(coll.isEmpty());//ture
    
        }
    
    }

> 结果  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 2]

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#### 二、 ####

**（一）**

> Person类+CollectionTest类

package com.mjl;
    
    import com.jh.Person;
    import org.junit.Test;
    
    import java.util.ArrayList;
    import java.util.Collection;
    
    public class CollectionTest {
        
    
        @Test
        public void test() {
        
            Collection coll = new ArrayList();
    
            coll.add(123);
            coll.add(456);
            coll.add(new String("Tom"));
            coll.add(false);
    
            Person p = new Person("Jerry", 20);
            coll.add(p);
    
    
            //contains(Object obj):判断当前集合中是否包含obj
            boolean contains = coll.contains(123);
            System.out.println(contains);//true
            System.out.println(coll.contains(new String("Tom")));//true
    
            System.out.println(coll.contains(p));//true
        }

> 结果  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 3]

**（二）**

> System.out.println(coll.contains§);  
> 改为  
> System.out.println(coll.contains(new Person(“Jerry”, 20)));  
> Person类同上

package com.mjl;
    
    import com.jh.Person;
    import org.junit.Test;
    
    import java.util.ArrayList;
    import java.util.Collection;
    
    public class CollectionTest {
        
    
        @Test
        public void test() {
        
            Collection coll = new ArrayList();
    
            coll.add(123);
            coll.add(456);
            coll.add(new String("Tom"));
            coll.add(false);
    
            coll.add(new  Person("Jerry", 20));
    
    
            //contains(Object obj):判断当前集合中是否包含obj
            boolean contains = coll.contains(123);
            System.out.println(contains);//true
            System.out.println(coll.contains(new String("Tom")));//true
    
            System.out.println(coll.contains(new Person("Jerry", 20)));//false
    
        }
    }

> 结果

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 4]  
**（三）**

> 若希望将false改为true，需要重写Person中的equals  
> ![在这里插入图片描述][677f9c5b41f548828faa78714aa8b3dc.png]

package com.jh;
    
    public class Person {
        
    
        private String name;
        private int age;
    
        public Person() {
        
        }
    
        public Person(String name, int age) {
        
            this.name = name;
            this.age = age;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public int getAge() {
        
            return age;
        }
    
        public void setAge(int age) {
        
            this.age = age;
        }
    
        @Override
        public String toString() {
        
            return "Person{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    
        @Override
        public boolean equals(Object o) {
        
    
            //自己添加的，判断是否重写了equals
            System.out.println("Person equals()......");
    
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
    
            Person person = (Person) o;
    
            if (age != person.age) return false;
            return name != null ? name.equals(person.name) : person.name == null;
        }
    
    //    @Override
    //    public int hashCode() {
        
    //        int result = name != null ? name.hashCode() : 0;
    //        result = 31 * result + age;
    //        return result;
    //    }
    }

package com.mjl;
    
    import com.jh.Person;
    import org.junit.Test;
    
    import java.util.ArrayList;
    import java.util.Collection;
    
    public class CollectionTest {
        
    
        @Test
        public void test() {
        
            Collection coll = new ArrayList();
    
            coll.add(123);//第一次找
            coll.add(456);//第二次找
            coll.add(new String("Tom"));//第三次找
    
    
            coll.add(new Person("Jerry", 20));//找到
    
            coll.add(false);
    
            //contains(Object obj):判断当前集合中是否包含obj
            //我们在判断时会调用obj对象所在类的equals()
    
            boolean contains = coll.contains(123);
            System.out.println(contains);
            System.out.println(coll.contains(new String("Tom")));
    
            System.out.println(coll.contains(new Person("Jerry", 20)));
    
        }
    }

##### 向Collection接口的实现类的对象中添加数据obj时，要求obj所在类要重写equals(). #####

> 结果  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 5]

**（四）**

> containsAll(Collection coll1):判断形参coll1中的所有元素是否都存在于当前集合中。

package com.mjl;
    
    import com.jh.Person;
    import org.junit.Test;
    
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.Collection;
    
    public class CollectionTest {
        
    
        @Test
        public void test() {
        
            Collection coll = new ArrayList();
    
            coll.add(123);//第一次找
            coll.add(456);//第二次找
            coll.add(new String("Tom"));//第三次找
    
    
            coll.add(new Person("Jerry", 20));//找到
    
            coll.add(false);
    
            //contains(Object obj):判断当前集合中是否包含obj
            //我们在判断时会调用obj对象所在类的equals()
    
            boolean contains = coll.contains(123);
            System.out.println(contains);
            System.out.println(coll.contains(new String("Tom")));
    
            System.out.println(coll.contains(new Person("Jerry", 20)));
    
            //2.containsAll(Collection coll1):判断形参coll1中的所有元素是否都存在于当前集合中。
            Collection coll1 = Arrays.asList(123,415);
            System.out.println(coll.containsAll(coll1));
        }
    }

> 结果  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 6]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/89bfe064733e48f4aa8141b174a56c78.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/21223daed96d4adb86a0bea5beec2c62.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/52d3966d6fed4e53b95b0c1aac2dfde3.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 3]: https://img-blog.csdnimg.cn/59c9e766fbfc4f9eb6225849467e62df.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 4]: https://img-blog.csdnimg.cn/f222de4b80c7474cacd17a1e085e8104.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[677f9c5b41f548828faa78714aa8b3dc.png]: https://img-blog.csdnimg.cn/677f9c5b41f548828faa78714aa8b3dc.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 5]: https://img-blog.csdnimg.cn/9b56127b17964b378a0e1cbc73ba292b.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 6]: https://img-blog.csdnimg.cn/e7d77929f23e43668ee771d445cdf7b7.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70