原文： https://beginnersbook.com/2013/12/java-arraylist-contains-method-example/
ArrayList contains()方法用于检查给定列表中指定的元素是否存在。
public boolean contains(Object element)
如果在列表中找到指定的元素，则返回true，否则返回false。
在这个例子中，我们有两个ArrayList（ArrayList<String>和ArrayList<Integer>），我们正在检查两个列表中是否存在少量元素。
package beginnersbook.com;
import java.util.ArrayList;
public class ContainsExample {
public static void main(String[] args) {
ArrayList<String> al = new ArrayList<String>();
al.add("pen");
al.add("pencil");
al.add("ink");
al.add("notebook");
System.out.println("ArrayList contains the string 'ink pen': "
+al.contains("ink pen"));
System.out.println("ArrayList contains the string 'pen': "
+al.contains("pen"));
System.out.println("ArrayList contains the string 'pencil': "
+al.contains("pencil"));
System.out.println("ArrayList contains the string 'book': "
+al.contains("book"));
ArrayList<Integer> al2 = new ArrayList<Integer>();
al2.add(1);
al2.add(99);
al2.add(56);
al2.add(13);
al2.add(44);
al2.add(6);
System.out.println("'1' is present in arraylist: "+al2.contains(1));
System.out.println("'55' is present in arraylist: "+al2.contains(55));
System.out.println("'44' is there in arraylist: "+al2.contains(44));
System.out.println("'7' is there in arraylist: "+al2.contains(7));
}
}输出：
ArrayList contains the string 'ink pen': false
ArrayList contains the string 'pen': true
ArrayList contains the string 'pencil': true
ArrayList contains the string 'book': false
'1' is present in arraylist: true
'55' is present in arraylist: false
'44' is there in arraylist: true
'7' is there in arraylist: false