问题是 if 3 == 3 部分后的括号分组

The problem is the parentheses grouping after the if 3==3 part.

当解析 set JAVA_HOME =％SUN_JAVA_HOME％命令时，解释器立即替换％SUN_JAVA_HOME％变量，这会导致（386）中右括号的早期匹配。

While parsing the set JAVA_HOME=%SUN_JAVA_HOME% command, the interpreter immediately replaces the %SUN_JAVA_HOME% variable and that causes an early match of the closing parenthesis in (386).

如果启用延迟了扩展，并将％SUN_JAVA_HOME％替换为！SUN_JAVA_HOME！：

This can be avoided if you enable delayed expansion and replace %SUN_JAVA_HOME% with !SUN_JAVA_HOME!:

setlocal enabledelayedexpansion

set SUN_JAVA_HOME=C:\Program Files (x86)\Java\jdk1.6.0_17

if 3==3 (
    set JAVA_HOME=!SUN_JAVA_HOME!
)
echo ready