Collection接口的基本方法如下:
add();size();contains();remove();isEmpty();clear();addAll();removeAll();retainAll();toArray();
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
public class Collectionexample {
public static void main(String[] args) {
Collection collection=new ArrayList();
// 当你向集合当中添加基本数据类型的时候 系统会帮你进行自动装箱
// 把基本数据类型变成它的包装类
boolean add=collection.add("a");
boolean add2=collection.add("b");
boolean add3=collection.add("c");
boolean add4=collection.add(10);
boolean add5=collection.add(true);
System.out.println(collection);
System.out.println(add);
System.out.println(add2);
System.out.println(add3);
System.out.println(add4);
System.out.println(add5);
// 获取集合的长度
System.out.println(collection.size());
// 判断是否包含某个元素
boolean contains=collection.contains("d");
System.out.println(contains);
// 从集合中删除一个元素
boolean remove=collection.remove("a");
System.out.println(collection);
System.out.println(remove);
// 判断集合是否为空
boolean empty=collection.isEmpty();
System.out.println(empty);
// 清空 集合
//collection.clear();
//System.out.println(collection);
/****addAll\removeAll\retainAll****/
System.out.println(collection);
Collection collection1=new ArrayList();
collection1.add("x");
collection1.add("y");
collection1.add("z");
System.out.println(collection1);
// addAll方法是 把集合collection的元素取出来加在集合collection1的末尾
collection1.addAll(collection);
System.out.println(collection1);
// add 是把集合collection中所有元素 以元素的形式放入集合collection1中
collection1.add(collection);
System.out.println(collection1);
//判断collection1中是否包含collection中的所有元素
boolean containsAll=collection1.containsAll(collection);
System.out.println(containsAll);
// removeAll 删除 集合collection2 与 集合collection 的重合元素,另一个集合不变只删除交集,重复也可以删除
Collection collection2=new ArrayList();
collection2.add("a");
collection2.add("b");
collection2.add("c");
collection2.add("d");
System.out.println(collection2);
collection2.removeAll(collection);
System.out.println(collection2);
// retainAll 把两个集合的交集取出来 保存在调用的集合
Collection collection3=new ArrayList();
collection3.add("a");
collection3.add("b");
collection3.add("c");
collection3.add("d");
System.out.println(collection3);
collection3.retainAll(collection);
System.out.println(collection3);
/*****toArray*****/
Collection collection4=new ArrayList();
collection4.add("a");
collection4.add("b");
collection4.add("c");
collection4.add("d");
// 集合转成数组
Object[] array=collection4.toArray();
for(int i=0;i<array.length;i++) {
System.out.println(array[i]);
}
Collection collection5=new ArrayList();
collection5.add(new Student("ysg",18));
collection5.add(new Student("sxm",18));
collection5.add(new Student("dp",18));
// 集合转数组 相当于 有一个向上转型
Object[] array1=collection5.toArray();
for(int i=0;i<array1.length;i++) {
Student student=(Student)array1[i];
System.out.println(student.getName());
}
/***迭代器***/
Collection collection6=new ArrayList();
collection6.add("a");
collection6.add("b");
collection6.add("c");
collection6.add("d");
// 获取集合中的迭代器
Iterator iterator =collection6.iterator();
//先判断集合中是否有元素
boolean hasNext=iterator.hasNext();
System.out.println(hasNext);
// 从集合中取出元素
Object next=iterator.next();
System.out.println(next);
//第二种遍历方法
while(iterator.hasNext()) {
Object next1=iterator.next();
System.out.println(next1);
}
Collection collection7=new ArrayList();
collection7.add(new Student("abc",18));
collection7.add(new Student("def",18));
collection7.add(new Student("hig",18));
Iterator iterator2=collection.iterator();
while(iterator2.hasNext()) {
Object next2=iterator.next();
Student student=(Student)next2;
System.out.println(student.getName());
}
}
}
运行结果:
[a, b, c, 10, true]
true
true
true
true
true
5
false
[b, c, 10, true]
true
false
[b, c, 10, true]
[x, y, z]
[x, y, z, b, c, 10, true]
[x, y, z, b, c, 10, true, [b, c, 10, true]]
true
[a, b, c, d]
[a, d]
[a, b, c, d]
[b, c]
a
b
c
d
ysg
sxm
dp
true
a
b
c
d
Exception in thread "main" java.util.NoSuchElementException
at java.util.ArrayList$Itr.next(ArrayList.java:860)
at Collectionexample.main(Collectionexample.java:143)
同一个包中的Student类:
public class Student {
String name;
int age;
public Student(String name) {
this.name=name;
}
public Student(String name,int age) {
this.name=name;
this.age=age;
}
public void setName(String name) {
this.name=name;
}
public String getName() {
return name;
}
public static void main(String[] args) {
Student student=new Student("xyz",18);
System.out.println(student.getName());
}
}
参考:
https://blog.csdn.net/Dzy_water/article/details/79100951