안드로이드 스튜디오 자바 문법

1) 형식 변환하기

    Button button1, button2,button3, button4, button5;
    TextView tv1, tv2, tv3, tv4, tv5;
    Integer var1;
    float var2;
    double var3;
    char var4;
    String var1Str, var2Str, var3Str, var4Str, var5Str;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button1 = (Button) findViewById(R.id.button1);
        button2 = (Button) findViewById(R.id.button2);
        button3 = (Button) findViewById(R.id.button3);
        button4 = (Button) findViewById(R.id.button4);
        button5 = (Button) findViewById(R.id.button5);
        tv1 = (TextView) findViewById(R.id.textView);
        tv2 = (TextView) findViewById(R.id.textView2);
        tv3 = (TextView) findViewById(R.id.textView3);
        tv4 = (TextView) findViewById(R.id.textView4);
        tv5 = (TextView) findViewById(R.id.textView5);

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                var1 = 10;
                var1Str = var1.toString();
                tv1.setText(var1Str);
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                var2 = 10.1f;
                var2Str = Float.toString(var2);
                tv2.setText(var2Str);
            }
        });

        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                var3 = 10.2;
                var3Str = Double.toString(var3);
                tv3.setText(var3Str);
            }
        });

        button4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                var4 = '안';
                var4Str = Character.toString(var4);
                tv4.setText(var4Str);
            }
        });

        button5.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                var5Str = "안드로이드";
                tv5.setText(var5Str);
            }
        });
    }
}

 

2) editText와 if 조건문 사용

 

    Button button1, button2;
    EditText edit1;
    TextView tv1;
    Integer count;
    String num1Str;
    ImageView imageView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button1 = (Button) findViewById(R.id.button1);
        edit1 = (EditText) findViewById(R.id.edit1);
        tv1 = (TextView) findViewById(R.id.textView);
        imageView = (ImageView) findViewById(R.id.image);

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // int count = 85;
                num1Str = edit1.getText().toString();  // 에디트 텍스트에서 데이터 가져오기
                count = Integer.parseInt(num1Str);  // 문자열을 정수로 변환하기
                if (count == -99) {
                    tv1.setText("종료");
                    imageView.setImageResource(0);
                } else if (count >= 90) {
                    tv1.setText("합격 (장학생)");
                    imageView.setImageResource(R.drawable.nnice);
                } else if (count >= 60) {
                    tv1.setText("합격");
                    imageView.setImageResource(R.drawable.nice);
                } else {
                    tv1.setText("불합격");
                    imageView.setImageResource(R.drawable.bad);
                }
            }
        });
    }
}

2-2) 위의 코드를 switch문으로 표현하기

 button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // int count = 85;
                num1Str = edit1.getText().toString();  // 에디트 텍스트에서 데이터 가져오기
                count = Integer.parseInt(num1Str);  // 문자열을 정수로 변환하기
                if (count == -99) {
                    tv1.setText("if-종료");
                    imageView.setImageResource(0);
                } else if (count >= 90) {
                    tv1.setText("if-합격 (장학생)");
                    imageView.setImageResource(R.drawable.nnice);
                } else if (count >= 60) {
                    tv1.setText("if-합격");
                    imageView.setImageResource(R.drawable.nice);
                } else {
                    tv1.setText("if-불합격");
                    imageView.setImageResource(R.drawable.bad);
                }
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                num1Str = edit1.getText().toString();
                count = Integer.parseInt(num1Str);
                var1 = (count / 10) * 10;
                switch(var1){
                    case 100: case 90:
                        tv2.setText("switch-합격(장학생)");
                        imageView.setImageResource(R.drawable.nnice);
                        break;
                    case 80: case 70: case 60:
                        tv2.setText("switch-합격");
                        imageView.setImageResource(R.drawable.nice);
                        break;
                    default:
                        tv2.setText("switch-불합격");
                        imageView.setImageResource(R.drawable.bad);
                }
            }
        });
    }
}

 

3) 반복문을 for문, while문으로 표현하기

    Button button1, button2;
    TextView tv1, tv2;
    Integer var1, j;
    String intTotal, intTotal2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button1 = (Button) findViewById(R.id.button1);
        button2 = (Button) findViewById(R.id.button2);
        tv1 = (TextView) findViewById(R.id.textView);
        tv2 = (TextView) findViewById(R.id.textView2);

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int one[] = new int[3];
                intTotal = "";
                for (int i=0; i<one.length; i++) {
                    one[i] = 10 * i;
                    intTotal = intTotal + "\n" + one[i];
                }
                tv1.setText("for문 수행 후 출력\n"+intTotal);
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int one[] = new int[3];
                intTotal2="";

                int j=0;
                while (j<one.length) {
                    one[j] = 10 * j;
                    intTotal2 = intTotal2 + "\n" + one[j];
                    j++;
                }
                tv2.setText("while문 수행 후 출력\n" + intTotal2);
            }
        });
    }
}

 

4) 함수 이용하여 표현하기

public class MainActivity extends AppCompatActivity {
    Button button1, button2;
    TextView tv1, tv2;
    static Integer var = 100;
    String tempStr, tempStr2;

    static Integer addFOO(Integer num1, Integer num2) { //함수
        Integer hap;
        hap = num1 + num2 + var;
        return hap;
    }

    static Integer subFOO(Integer num1, Integer num2) { //함수
        Integer hap;
        hap = num1 - num2 + var;
        return hap;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button1 = (Button) findViewById(R.id.button1);
        button2 = (Button) findViewById(R.id.button2);
        tv1 = (TextView) findViewById(R.id.textView);
        tv2 = (TextView) findViewById(R.id.textView2);

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Integer sum = addFOO(10, 20);
                tempStr = sum.toString();
                tv1.setText("addFOO 출력\n"+tempStr);
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Integer sub = subFOO(10, 20);
                tempStr2 = sub.toString();
                tv2.setText("subFOO 출력\n"+tempStr2);
            }
        });
    }
}