Collection集合常用API

By xyp-hf

Update date:

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public class TestCollection {

	public static void main(String[] args) {
		
		//获取Collection集合的引用
		//Collection c1 = new Collection(); error 接口不能构造对象
		//接口类型的引用指向了实现类的对象，形成了多态
		Collection c1 = new ArrayList();
		
		//向集合c1中增加元素
		boolean b1 = c1.add(new Integer(1));
		System.out.println("b1 = " + b1); //true
		//自动调用toString()，编译器自动添加
		//在编译阶段调用父类的方法，在运行阶段调用子类重写以后的方法，ArrayList类
		//toString()方法默认打印的格式为：[元素1, 元素2, ...]
		System.out.println("c1 = " + c1); //[1]
		
		b1 = c1.add(new String("two"));
		System.out.println("b1 = " + b1); //true
		System.out.println("c1 = " + c1); //[1, two]
		
		b1 = c1.add(new Student(1001, "zhangfei", 30));
		System.out.println("b1 = " + b1); //true
		//当打印集合中的元素时，本质上调用每个元素对应的toString()来打印
		//[1, two, Student[id=1001, name=zhangfei, age=30]]
		System.out.println("c1 = " + c1); 
		
		System.out.println("--------------------------------------");
		//准备另外一个集合
		Collection c2 = new ArrayList();
		c2.add(3); //采用了自动装箱技术 int => Integer
		System.out.println("c2 = " + c2); //[3]
		c2.add("four");
		System.out.println("c2 = " + c2); //[3, four] 
		System.out.println("当前集合的元素个数是：" + c2.size()); //2
		System.out.println("当前集合的元素个数是：" + c1.size()); //3
		
		System.out.println("--------------------------------------");
		//将集合c2中的所有元素添加到集合c1中，本质上就是将c2的元素一个个取出来放入c1
		b1 = c1.addAll(c2);
		//本质上将c2看做一个元素，然后整体放入c1中
		//b1 = c1.add(c2);
		System.out.println("b1 = " + b1); //b1 = true
		//[1, two, Student[id=1001, name=zhangfei, age=30], 3, four]
		//[1, two, Student[id=1001, name=zhangfei, age=30], [3, four]]
		System.out.println("c1 = " + c1); 
		System.out.println("c2 = " + c2); //[3, four] 
		
		System.out.println("--------------------------------------");
		//判断集合c1中是否包含参数指定的单个元素
		//[1, two, Student[id=1001, name=zhangfei, age=30], 3, four]
		b1 = c1.contains(new Integer(1));
		System.out.println("b1 = " + b1); //b1 = true
		b1 = c1.contains(new Integer(2));
		System.out.println("b1 = " + b1); //b1 = false
		b1 = c1.contains(new String("two"));
		System.out.println("b1 = " + b1); //b1 = true
		//contains方法的原理：参数对象调用equals()方法与集合中的元素一个一个比较
		//当Student类没有重写equals()方法时，则比较对象的地址，因此结果为false
		//当Student类重写equals()方法后，则比较对象的内容，因此结果为true
		b1 = c1.contains(new Student(1001, "zhangfei", 30));
		System.out.println("b1 = " + b1); //false  b1 = true 
		
		System.out.println("--------------------------------------");
		//判断集合c1中是否包含参数指定的多个元素
		//[1, two, Student[id=1001, name=zhangfei, age=30], 3, four]
		//将集合c2中的元素一个个拿出来在c1中进行查找
		//[3, four] 
		//b1 = c1.containsAll(c2);
		//表示判断集合c1中是否有元素c2这个整体
		b1 = c1.contains(c2);
		System.out.println("b1 = " + b1); //b1 = true false
		
		System.out.println("--------------------------------------");
		//实现集合c1中单个元素的删除
		b1 = c1.remove(new String("2"));
		System.out.println("b1 = " + b1); //b1 = false
		//[1, two, Student[id=1001, name=zhangfei, age=30], 3, four]
		System.out.println("c1 = " + c1); //
	
		b1 = c1.remove(new String("two"));
		System.out.println("b1 = " + b1); //b1 = true
		//[1, Student[id=1001, name=zhangfei, age=30], 3, four]
		System.out.println("c1 = " + c1); //
		
		System.out.println("--------------------------------------");
		//[1, Student[id=1001, name=zhangfei, age=30], 3, four]
		System.out.println("c1 = " + c1); //
		//[3, four] 
		System.out.println("c2 = " + c2);
		
		//实现集合c1中多个元素的删除
		//表示从集合c1中将集合c2中的元素一个一个删除
		b1 = c1.removeAll(c2);
		//表示从集合c1中将集合c2这个元素整体删除
		//b1 = c1.remove(c2);
		System.out.println("b1 = " + b1); //true  false
		//[1, Student[id=1001, name=zhangfei, age=30], 3, four]
		System.out.println("c1 = " + c1); //[1, Student[id=1001, name=zhangfei, age=30]]
		System.out.println("c2 = " + c2); //[3, four]
		
		System.out.println("--------------------------------------");
		//实现集合c1中所有元素的删除
		//c1.clear();
		//System.out.println("c1 = " + c1); //[啥也没有]
		//System.out.println(c1.isEmpty()); //true
		//System.out.println(c1.size()); //0
		
		System.out.println("--------------------------------------");
		//计算两个集合的交集并保留到当前集合中
		System.out.println("c1 = " + c1); //[1, Student[id=1001, name=zhangfei, age=30]]
		System.out.println("c2 = " + c2); //[3, four]
		
		//计算c1和c2的交集并保留到c1中，若c1集合中的内容发生了改变则返回true
		b1 = c1.retainAll(c2);
		System.out.println("b1 = " + b1); //true
		System.out.println("c1 = " + c1); //[啥也没有]
		System.out.println("c2 = " + c2); //[3, four]
		
		System.out.println("--------------------------------------");
		//计算两个集合的交集并保留到当前集合中
		//计算c2和c2的交集并保留到c2中，c2中的内容不发生改变，因此返回false
		b1 = c2.retainAll(c2);
		System.out.println("b1 = " + b1); //false
		System.out.println("c2 = " + c2); //[3, four]
	}

}
JAVA
集合