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Object obj = "hello 14";// Jdk之前版本if (obj instanceof String) { String str = (String) obj; System.out.println("str length:" + str.length());} else { System.out.println("obj not string.");}
// Jdk14版本if (obj instanceof String str) { System.out.println("str length:" + str.length());} else { System.out.println("obj not string.");}

String str = null;System.out.println(str.length());
/** * Jdk之前版本异常输出: * Exception in thread "main" java.lang.NullPointerException * at DemoNull.main(DemoNull.java:9) */
/** * Jdk14版本异常输出: * Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.length()" because "str" is null * at DemoNull.main(DemoNull.java:9) */

/** * @author liujiazhong */public final class Order {
 private final Long orderId; private final String orderCode;
 public Order(Long orderId, String orderCode) { this.orderId = orderId; this.orderCode = orderCode; }
 public Long getOrderId() { return orderId; }
 public String getOrderCode() { return orderCode; }
 @Override public boolean equals(Object o) { if (this == o) return true; if (!(o instanceof Order)) return false; Order order = (Order) o; return Objects.equals(getOrderId(), order.getOrderId()) && Objects.equals(getOrderCode(), order.getOrderCode()); }
 @Override public int hashCode() { return Objects.hash(getOrderId(), getOrderCode()); }
 @Override public String toString() { return "Order{" + "orderId=" + orderId + ", orderCode='" + orderCode + '\'' + '}'; }}
/** * @author liujiazhong */public record RecordOrder(Long orderId, String orderCode) {}
// 测试Order order1 = new Order(1001L, "TEST1001");RecordOrder order2 = new RecordOrder(1002L, "TEST1002");System.out.println(order1);System.out.println(order2);System.out.println(order1.getOrderCode());System.out.println(order2.orderCode());
// 结果Order{orderId=1001, orderCode='TEST1001'}RecordOrder[orderId=1002, orderCode=TEST1002]TEST1001TEST1002
// 可以定义其他信息public record RecordOrder(Long orderId, String orderCode) {
 public static final String TYPE = "online";
 public RecordOrder() { this(1003L, "TEST1003"); }
 public static void printType() { System.out.println(TYPE); }
 public void printOrderCode() { System.out.println(orderCode); }
}

String str = "A";// Jdk之前的版本switch (str) { case "A": System.out.println("A");break; case "B": System.out.println("B");break; default: System.out.println("default");}
// Jdk12之后switch (str) { case "A", "C" -> System.out.println("A || C"); case "B" -> System.out.println("B"); default -> System.out.println("default");}
// yield用于返回值int score = switch (str) { case "A" -> 90; case "B" -> 80; default -> { System.out.println("default"); yield 70; }};System.out.println(score);

/** * 在Jdk14中通过-XX:+UseConcMarkSweepGC选项尝试使用CMS的话会得到下面的警告信息 * Java HotSpot(TM) 64-Bit Server VM warning: Ignoring option UseConcMarkSweepGC; support was removed in 14.0 */List<String> list = new ArrayList<>();while (true) { list.add("a");}

/** * -XX:+UnlockExperimentalVMOptions -XX:+UseZGC */List<String> list = new ArrayList<>();while (true) { list.add("a");}

/** * 使用-XX:+UseParallelGC -XX:-UseParallelOldGC或者-XX:-UseParallelOldGC参数启用组合后提示以下信息 * Java HotSpot(TM) 64-Bit Server VM warning: Option UseParallelOldGC was deprecated in version 14.0 and will likely be removed in a future release. */public static void main(String[] args) { List<String> list = new ArrayList<>(); while (true) { list.add("a"); }}

// Jdk之前的版本String sql1 = "select\n" + "\t*\n" + "from\n" + "\tord_order_item ooi\n" + "left join ord_order oo on\n" + "\tooi.order_id = oo.id\n" + "where\n" + "\too.order_code = 'TEST1001'\n" + "order by\n" + "\too.id desc";
// 三引号表示文本块String sql2 = """ select * from ord_order_item ooi left join ord_order oo on ooi.order_id = oo.id where oo.order_code = 'TEST1001' order by oo.id desc """;
// 新增“\s”表示空格，“\”表示去除换行String sql3 = """ select * from ord_order_item ooi left join ord_order oo on ooi.order_id = oo.id where oo.order_code = 'TEST1001' order by\s\ oo.id desc """;System.out.println(sql1);System.out.println(sql2);System.out.println(sql3);