实现原理：

 这是第一个头结点，现在要插入一个节点，也就是让新节点指向该头结点，任何让head指向新节点，新节点变为头结点。

代码实现：

 实体类：

public class entity {private String data;private entity next;public entity() {}public entity(entity next) {this.next = next;}public entity(String data, entity next) {this.data = data;this.next = next;}public String getData() {return data;}public void setData(String data) {this.data = data;}public entity getNext() {return next;}public void setNext(entity next) {this.next = next;}
}

头插法：

public class function {public static void main(String[] args) {entity head = new entity("1", null);head = add(head,"2");head = add(head,"3");show(head);}//遍历public static void show(entity entity) {System.out.println(entity.getData());if (entity.getNext() != null) {show(entity.getNext());} else {return;}}//头插法插入public static entity add(entity head,String data) {entity entity = new entity(data, head);head = entity;return head;}}