OnClickListener onClickListener = new OnClickListener() {
    @Override
    public void onClick(View v) {
        startActivity(new Intent(action));
    }
};

Button button = (Button) findViewById(id);
button.setOnClickListener(onClickListener);

startActivity(new Intent(this, ActivityToLaunch.class));

Button x.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v)
                {
                    Intent i = new Intent(y.this, Activity.class);
                    startActivity(i);
                }
        });

Button btn = (Button)findViewById(R.id.button1);

btn.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {

        startActivity(new Intent(TestActivity.this,second.class));

    }
});

public void onClick(View v)
{
    Intent myintent = new Intent(currentclass.this, nextactivity.class);
    startActivity(myintent);
}

final Context cont = this;
Button btnClickABC =(Button)findViewById(R.id.btnClickABC);
btnClickABC.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                startActivity(new Intent(cont, NextActivity.class));

            }
        });

Intent(PresentActivity.this, NextActivity.class)

public class PresentActivity extends Activity {
        protected void onCreate(Bundle icicle) {
            super.onCreate(icicle);

            setContentView(R.layout.content_layout_id);

            final Button button = (Button) findViewById(R.id.button_id);
            button.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    // Perform action on click

                    Intent activityChangeIntent = new Intent(PresentActivity.this, NextActivity.class);

                    // currentContext.startActivity(activityChangeIntent);

                    PresentActivity.this.startActivity(activityChangeIntent);
                }
            });
        }
    }

Button button = (Button)findViewById(R.id.xxx);
    button .setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
        Intent intent=new Intent(CurrentActivity.this,NextActivity.class);
        startActivity(intent);
        }
    });

startActivity(new Intent(this,newActivity.class));

<activity
  android:name=".Tester"
  android:label="@string/title_activity_tester" >`enter code here`
</activity>


final Button button = (Button) findViewById(R.id.btnGo);// btnGo is id
button.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        Intent i = new Intent(CurrentClass.this, Tester.class);
        startActivity(i);
    }

startActivity(Intent(this, LoginActivity::class.java))

startActivity(new Intent(this, LoginActivity.class))