boolean b = false;

if (b = true){
    System.out.println("true");
}else{
    System.out.println("false");
}

true is output

switch

Compile error when defining the same case more than once
Works normally even with default at the beginning
Compile error if the type of the target variable and the type of the branch destination variable do not match (there is implicit type conversion)
Available types are byte, short, int, char, String, enum

while

int i = 0;
while(i++ < 10);{
    System.out.println("a");
}

Is only incremented by i.

break Only loops (for, while) and switches can be used

constructor

This. Variable cannot be used as an argument of this ().

class Orange{
    int i;

    Orange(){
        this(this.i);
    } 

    Orange(int i){}
}

Initialization of arrays and variable containers (StringBuilder, List)

	public static void main(String[] args) {
		String ary[] = new String[3];
		System.out.println(ary.length);  // => 3
		
		StringBuilder sb = new StringBuilder(3);
		System.out.println(sb.length());  // => 0
		
		List<String> list = new ArrayList<String>(3);
		System.out.println(list.size());  // => 0
	}

Generics


public interface Portable<Integer>{
    public void handCarry(Integer weight);
}

When using a lambda expression

NG pattern

Portable p = (Integer w) -> System.out.println(w);

OK pattern


Portable<Integer> p = (Integer w) -> System.out.println(n);

Portable p = w -> System.out.println(w);

The order is maintained when using Stream's paralell () and reduce () in combination.


System.out.println(Stream.of("a", "b", "c", "d").parallel().reduce((x,y)->x+"-"+y).get());  // =>Always a-b-c-d

Stream.of("a", "b", "c", "d").parallel().forEach(System.out::print);  // =>In no particular order a, b, c,d is output

Java basic syntax + α trap

constructor

Initialization of arrays and variable containers (StringBuilder, List)

Generics

NG pattern

OK pattern

The order is maintained when using Stream's paralell () and reduce () in combination.