Strange Behaviors in Java: Integer Caching, String Comparison, Unary Plus, and Unicode Tricks

Java contains several surprising language features that often confuse developers. This article walks through four such quirks with clear explanations and runnable examples.

1. Integer caching – Java caches Integer objects in the range [-128, 127] by default, causing a == b to be true for values within the cache. The upper bound can be changed via the JVM property -Djava.lang.Integer.IntegerCache.high=300 , as shown in the following code:

public static void main(String[] args) {
    Integer a = 120;
    Integer b = 120;
    Integer c = 130;
    Integer d = 130;
    System.out.println(a == b); // true
    System.out.println(c == d); // false
}

When the property is set to a higher value, both comparisons become true because the cache range expands.

2. String comparison – Literal strings are interned in the constant pool, so s1 == s2 yields true, while new String("hello") creates distinct objects, making s3 == s4 false. The intern() method can force a string into the pool.

public static void main(String[] args) {
    String s1 = "hello";
    String s2 = "hello";
    String s3 = new String("hello");
    String s4 = new String("hello");
    System.out.println(s1 == s2); // true
    System.out.println(s3 == s4); // false
}

3. Unary plus is not an operator – In the statement i =+ 2 , the + is a sign, not a binary addition operator, so the variable becomes 2 instead of 102 . Changing it to - would assign -2 .

public static void main(String[] args) {
    int i = 100;
    i =+ 2; // i becomes 2
    System.out.println(i);
}

4. Unicode escapes in comments – Unicode escape sequences are processed before compilation, even inside comments. The sequence \u000d turns a comment line into executable code, causing System.out.println("Hello World!"); to run despite appearing commented.

public static void main(String[] args) {
    // \u000d System.out.println("Hello World!");
}

These examples highlight the importance of understanding Java’s low‑level details to avoid unexpected behavior.