The expression in an if statement must be a boolean expression. : if « Statements « SCJP

1. SCJP
2. Statements
3. if

public class MainClass{
    public static void main(String[] argv){
        int y = 5;
        int x = 2;
        if (((x > 3) && (y < 2)) | doStuff()) {
           System.out.println("true");
        }
    }
    static boolean doStuff(){
      return true;
    }
}

public class MainClass{
    public static void main(String[] argv){
        int x = 3;
        if (x = 5) { }  // Won't compile because x is not a boolean!
    }
}

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	Type mismatch: cannot convert from int to boolean

	at MainClass.main(MainClass.java:4)