assert:
assert x <= 0;
if not equal by 0 then AssertionError
assert x <= 0 : "x must <= 0";
- 断言不能在可恢复的程序错误使用,只应该用于开发和测试阶段。
- 要执行assert语句,必须给 Java 虚拟机传递-enableassertions(参数启用断言,可简写为-ea)JVM 默认是关闭断言指令的。
java -ea Main.java

assert:
assert x <= 0;
if not equal by 0 then AssertionError
assert x <= 0 : "x must <= 0";
java -ea Main.java